Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC ANALYTICAL CHEMISTRY  

New moment equations were developed for size exclusion capillary electrochromatography (SECEC), in which intermolecular chemical reactions simultaneously took place. They explain how the first absolute and second central moments of elution peaks are correlated with some fundamental equilibrium and kinetic parameters of mass transfer and chemical reaction in SECEC column. In order to demonstrate the effectiveness of the moment equations, they were used to predict chromatographic behavior under hypothetical SECEC conditions. It was quantitatively studied how the association and dissociation rate constants of intermolecular interaction affected the position and spreading of elution peaks. It was indicated that both the intermolecular reaction kinetics and axial dispersion of solute molecules in a capillary column had a predominant contribution to the band broadening.

DOI： 10.2116/analsci.33.1147

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Affinity capillary electrophoresis (ACE) has been widely applied to evaluate binding constants of various systems. Recently, moment equations were derived based on the moment analysis (MA) theory for describing the influence of reaction kinetics and longitudinal diffusion on the elution peak profiles measured by ACE (MA-ACE). The equations enable one to obtain not only the binding constants but also the reaction rate constants from the migration time and variance of elution peaks. However, it is necessary to consider other factors (e.g., sample injection, detector window, Joule heating, and ramp time of the voltage increase) to improve the accuracy of MA-ACE. The variance of these effects was quantified under typical experimental conditions. Such quantification clarified the process to obtain the rate constants. The best experimental conditions to achieve high accuracy were discussed.

DOI： 10.1021/acs.analchem.7b02598

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：CHEMICAL SOC JAPAN  

The combination of moment analysis (MA) theory with affinity capillary electrophoresis (ACE) leads to a new method (MA-ACE) for the kinetic study of intermolecular interaction. The reaction rate constants, i.e., association (k(a)) and dissociation (k(d)) rate constants, can be analytically determined by the MA theory from the first absolute and second central moments of the elution peaks measured by ACE. In order to verify the validity of the MA-ACE method, the values of ka and kd were analytically determined for the formation and dissociation of the inclusion complex between thymol and sulfated-beta-cyclodextrin. The resulting values of k(a) and k(d) were comparable with those in our previous study, which were determined by chromatographic capillary electrophoresis with the MA theory. It was demonstrated that the MA-ACE method was effective for the kinetic study of intermolecular interactions. The rate constants can be analytically determined with no immobilization and no chemical modification, i.e., fluorescence labelling, of solute and ligand molecules.

DOI： 10.1246/bcsj.20160193

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：CHEMICAL SOC JAPAN  

We applied moment analysis (MA) with chromatographic capillary electrophoresis (CCE) to the analytical determination of rate constants (kin and kat) of solute permeation at the interface between a bulk solvent and surfactant micelles. CE experiments were carried out in the MEKC system using thymol and sodium dodecylsulfate (SDS) as the solute and surfactant, respectively, under CCE conditions. In CCE mode, experimental conditions are controlled so that the migration of micelles, which dissolve single or plural solute molecules, is stopped in the axial direction of a capillary. Only solute molecules migrate in the capillary and are detected to record elution peak profiles. The mass-transfer kinetics of solute molecules in the capillary are determined from the elution peak profiles by the MA theory. The values of k(in) and k(out) were respectively determined as 1.5 x 10(-6) and 2.6 x 10(-9)m s(-1) for the permeation of thymol molecules at the interfacial boundary of SDS micelle. It was demonstrated that MA-CCE was effective for the kinetic study of solute permeation across the interface between a bulk solvent and spherical molecular aggregates, e.g., surfactant micelles.

DOI： 10.1246/bcsj.20160185

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：CHEMICAL SOC JAPAN  

The moment analysis (MA) theory was introduced into the analysis of elution peak profiles measured by affinity capillary electrophoresis (ACE). New moment equations were developed, which were essential for analytically determining the association (k(a)) and dissociation (k(d)) rate constants of intermolecular interactions from the ACE data. The combination of the MA theory and ACE procedure leads to a method for the kinetic study of intermolecular interactions (MA-ACE). Because ACE has quite frequently been used for determining binding (association equilibrium) constants of intermolecular interactions, it must be important that k(a) and k(d) can also be determined from ACE elution peaks. An attempt was made to analyze ACE elution peaks in a published paper by the MA method to determine the rate constants. The values of k(a) and k(d) were analytically determined for the intermolecular interaction between three boronic acids and fructose. They were comparable with those determined by the other method based on the macroscopic approach for studying kinetics at equilibrium. It was demonstrated that the MA method was effective for extracting information about affinity kinetics of intermolecular interactions from elution peaks measured by ACE. This means that the MA method makes it possible to use ACE data previously published as a source for kinetic study of intermolecular interactions.

DOI： 10.1246/bcsj.20160068

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：CHEMICAL SOC JAPAN  

We developed a capillary electrophoretic (CE) method for the kinetic study of intermolecular interactions. Neither immobilization nor chemical modification, e.g., fluorescence labelling, of solute and ligand molecules is required. A concept of chromatographic capillary electrophoresis (CCE) was introduced as an experimental CE procedure. In the CCE mode, the migration of solute ligand complex in a capillary is stopped. Only solute molecules migrate and are detected. New moment equations were developed, which were essential for determining association and dissociation rate constants from elution peak profiles measured under the CCE conditions. The combination of the CCE concept and the moment theory leads to the CE method, i.e., moment analysis by CCE (MACCE). However, because it was hard to really perform CE experiments under the CCE conditions, we also developed practical experimental and data analysis procedures for the MACCE measurement. The reaction rate constants were analytically determined by the MACCE method for the formation and dissociation of the inclusion complex between thymol and sulfated-beta-cyclodextrin. It is unnecessary to fit elution curves numerically calculated to those experimentally measured for determining the rate constants. It was demonstrated that the MACCE method was effective for the kinetic study of intermolecular interactions.

DOI： 10.1246/bcsj.20150203

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC ANALYTICAL CHEMISTRY  

We developed moment analysis of affinity kinetics by chromatographic capillary electrophoresis (MKCCE) method for the kinetic study of intermolecular interactions. Association and dissociation rate constants of the interaction in a micellar electrokinetic chromatography (MEKC) system between thymol and sodium dodecylsulfate micelle were determined by the MKCCE method. It is a method based on the moment theory for the kinetic study of intermolecular interactions under the conditions that neither immobilization nor chemical modification of molecules is required. In CCE mode, experimental conditions are controlled so that the migration of solute-micelle complex is stopped and only solute molecules migrate in a capillary. Mass transfer behavior of solute molecules in the CCE system is analogous to that in a chromatographic system. However, because it was difficult in practice to really perform CE experiments under the CCE conditions, CE data were measured with changing experimental conditions, i.e., applied pressure, under the conditions that the migration velocity of solute-micelle complex was around zero. The rate constants could be analytically determined from the CE data. In the MKCCE method, it is not necessary to fit elution curves numerically calculated to those experimentally measured for the determination of the rate constants. Regarding the interaction between thymol and SDS association equilibrium constant and association and dissociation rate constants were determined as 6.35 x 10(3) dm(3) mol(-1), 5.6 x 10(4) dm(3) mol(-1) s(-1), and 8.7 s(-1), respectively. It was demonstrated that the MKCCE method was effective for the kinetic study of intermolecular interactions.

DOI： 10.2116/analsci.31.1019

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC ANALYTICAL CHEMISTRY  

The intermolecular interaction between 2-phenoxypropionic acid and beta-bromo-cyclodextrin affixed on the stationary phase surface in a chiral HPLC system was studied by the moment analysis method. At first, pulse response and peak parking experiments were conducted to measure some parameters concerning the column geometry, adsorption equilibrium, and mass-transfer kinetics. Then, the first absolute moment (mu(1)) and second central moment (mu(2)') of the elution peaks were analyzed by the moment equations, which were developed by assuming that the reaction kinetics between the solute molecules and the functional ligands can be represented by the Langmuir-type rate equation. Finally, the flow-rate dependence of HETP calculated from mu(1) and mu(2)' was analyzed by using the values of the parameters to determine the association and dissociation rate constants of the intermolecular interaction. It was demonstrated that the combination of the chromatographic experiments and moment analysis is one of the effective strategies for the kinetic study of intermolecular interactions.

DOI： 10.2116/analsci.31.743

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Moment equations were derived for chromatography, in which the reaction kinetics between solute molecules and functional ligands on the stationary phase was represented by the Langmuir type rate equation. A set of basic equations of the general rate model of chromatography representing the mass balance, mass transfer rate, and reaction kinetics in the column were analytically solved in the Laplace domain. The moment equations for the first absolute moment and the second central moment in the real time domain were derived from the analytical solution in the Laplace domain. The moment equations were used for predicting the chromatographic behavior under hypothetical HPLC conditions. The influence of the parameters relating to the adsorption equilibrium and to the reaction kinetics on the chromatographic behavior was quantitatively evaluated. It is expected that the moment equations are effective for a detailed analysis of the influence of the mass transfer rates and of the Langmuir type reaction kinetics on the column efficiency. (C) 2014 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.chroma.2014.06.052

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC ANALYTICAL CHEMISTRY  

The van Deemter equation and moment equations were used for analyzing the flow rate dependence of HETP experimentally measured in order to clarify chromatographic behavior from the kinetic points of view in columns packed with C-18-silica monolith and C-18-core-shell particles under RPLC conditions. They provided some information about molecular diffusion, eddy diffusion, and mass transfer kinetics in the columns. Additionally, the value of intra-stationary phase diffusivity was determined in the range of 10(-7) - 10(-6) cm(2) s(-1) by the moment analysis. Information about the contribution of the mass transfer resistance in the external liquid film around the stationary phase to HETP was also obtained. Its contribution increases with an increase in the flow velocity of the mobile phase. It was concluded that the moment equations can provide more detailed information about the kinetic behavior in the columns than the van Deemter equation.

DOI： 10.2116/analsci.30.277

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC ANALYTICAL CHEMISTRY  

This study was concerned about an estimation of molecular diffusivity (D-m) in liquid phase systems. An equation based on the absolute rate theory of diffusion was derived by considering the aggregation of not only solvent molecules, but also solute molecules. It was also studied how the replacement of the molar volume of a solvent with its molecular weight influences the accuracy in estimating D-m. The values of D-m estimated by the equation were compared with those experimentally measured. The mean square deviation for the estimation of D-m was calculated as being about 14% for 217 D-m data measured in aqueous solutions of methanol and acetonitrile, which is comparable to that obtained by the Wilke-Chang equation. However, D-m of some solutes in carbon tetrachloride was more accurately estimated by this equation than by the Wilke-Chang equation. It is expected that the equation proposed in this study is effective for estimating D-m in liquid phase systems.

DOI： 10.2116/analsci.29.467

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC ANALYTICAL CHEMISTRY  

It was demonstrated that the peak parking-moment analysis (PP-MA) method could be used as an alternative for the measurement of pore diffusivity (D-p) in porous packing materials for HPLC. The value of D-p of uracil was measured by the PP-MA method under non-retained conditions in the RPLC systems using C-18-silica gel particles and C-18-silica monolith as the stationary phase and 70 vol% methanol as the mobile phase. The value of D-p was compared with that derived by the pulse response-moment analysis (PR-MA) method under the same conditions. The D-p values of uracil derived by the PP-MA and PR-MA methods were almost in agreement with each other. Because the PP-MA and PR-MA methods have complementary characteristics as experimental methods for studying mass transfer kinetics, it is expected that the combination of the two methods would lead to an effective strategy for the measurement of Dp in porous separation media for HPLC.

DOI： 10.2116/analsci.29.315

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC ANALYTICAL CHEMISTRY  

Peak parking experiments were conducted to study the chromatographic behavior in a RPLC system consisting of a column packed with superficially porous C(18)-particles and a mixture of methanol and water (70/30, v/v). The values of the surface diffusion coefficient and the retention equilibrium constant of a column packed with superficially porous C(18)-particles were comparable to those of columns packed with a C(18)-silica monolith and full-porous C(18)-silica gel particles. The flow-rate dependence of HETP was hypothetically calculated by using moment equations to clarify the influence of the structural characteristics on the chromatographic behavior. The column efficiency of a column packed with the superficially porous particles is higher in the high flow-rate range than that with full-porous spherical particles. This is attributed to the smaller contribution of the intraparticulate mass transfer in the superficially porous particles to band broadening. The moment equations are effective for the quantitative analysis of chromatographic behavior of superficially porous particles.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-BLACKWELL  

It was tried to estimate the molecular diffusivity (D(m)) of solutes in the mixtures of acetonitrile (ACN) and water by the Wilke-Chang equation. Although the information about association coefficient (alpha) is necessary for the calculation, it has never been proposed for ACN. The value of alpha was estimated as 1.37 from D(m) of benzene in ACN at 303 K experimentally measured by the peak parking method. The values of alpha, i.e. 2.6, 1.9, 1.5, and 1.0, which have respectively been proposed for four solvents, i.e. water, methanol, ethanol, and benzene, were correlated with two physico-chemical parameters of the solvents, i.e. solubility parameter and E(T) value. The alpha value for ACN was plotted around the two correlations, indicating its appropriateness. The values of D(m) calculated by the Wilke-Chang equation using the alpha value for ACN were compared with those measured by the peak parking method and the Aris-Taylor method in aqueous solutions of ACN. The mean square deviation of the estimation of D(m) was calculated as 8.8 and 14%. It was demonstrated that the Wilke-Chang equation can be used for estimating D(m) with a reasonable accuracy in the mixtures consisting of ACN and water.

DOI： 10.1002/jssc.201100385

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC ANALYTICAL CHEMISTRY  

New moment equations were developed for chromatography using superficially porous (shell-type) spherical particles, which have recently attracted much attention as one of separation media for fast separation with high efficiency. At first, the moment equations of the first absolute and second central moments in the real time domain were derived from the analytical solution in the Laplace domain of a set of basic equations of the general rate model of chromatography, which represent the mass balance, mass-transfer rate, and reaction kinetics in the column packed with shell-type particles. Then, the moment equations were used for analyzing the experimental data of chromatography of kallidin in a Halo column, which were published in a previous paper written by other researchers. It was tried to predict the chromatographic behavior of shell-type particles having different shell thicknesses. The new moment equations are useful for a detailed analysis of the chromatographic behavior of shell-type spherical particles. It is also concluded that they can be used for the preliminarily optimization of their structural characteristics.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

This study deals with the application of the Wilke-Chang equation to the estimation of molecular diffusivity (D(m)) in liquid phase systems including polar solutes and/or solvents. First, D(m) of benzene in six different organic solvents was experimentally measured by the peak parking method. The value of association coefficient (alpha) was calculated from the D(m) values by assuming that D(m) can be represented by the Wilke-Chang equation. Then, them alpha value was correlated with the solubility parameter (delta) and E(T) of the solvents. Two different curved correlations were observed between alpha and the two physico-chemical parameters. This means that alpha of given solutes and solvents can be obtained from the values of delta and/or E(T). Finally, D(m) was estimated by a modified Wilke-Chang equation, which is derived by considering the aggregation of not only solvent molecules but also solute molecules. Although alpha is necessary for the estimation, it was calculated from delta for various solutes and solvents. The D(m) values estimated were compared with those reported in literature. The mean square deviation between the D(m) values was calculated less than 19% for 71 D(m) data. It was demonstrated that the modified Wilke-Chang equation can be used for estimating D(m) in liquid phase systems containing polar solutes and solvents. (C) 2011 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.chroma.2011.07.018

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER HEIDELBERG  

This study is concerned with the explanation of some thermodynamic properties of the retention equilibrium on a C-18-silica monolithic column. Pulse response experiments were carried out in a reversed-phase liquid chromatography system using a methanol/water mixture (70/30, v/v) and n-alkylbenzene homologs as the mobile phase and sample compounds, respectively, in the temperature range between 278 and 318 K. The retention equilibrium constant (K-a) was calculated from the first absolute moment of elution peaks. The dependence of K-a on the column temperature was analyzed using the modified van't Hoff plot proposed by Krug et al. to derive the changes of the Gibbs free energy, the enthalpy and the entropy concerning the retention behavior. First, the presence of a real enthalpy-entropy compensation (EEC) for the retention equilibrium was demonstrated. Then, a thermodynamic model based on the real EEC was developed to explain the temperature dependence of the linear free energy relationship (LFER) of the retention equilibrium. The model indicates how the slope and intercept of the LFER are correlated with the compensation temperatures and several molecular thermodynamic parameters. The model was effective for explaining the thermodynamic properties of the retention equilibrium of the C18-silica monolithic stationary phase.

DOI： 10.1007/s10337-011-2062-y

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Chromatographic properties of a new type of monolithic silica rod columns were examined. Silica rod columns employed for the study were prepared from tetramethoxysilane, modified with octadecylsilyl moieties, and encased in a stainless-steel protective column with two polymer layers between the silica and the stainless-steel tubing. A 25 cm column provided up to 45,000 theoretical plates for aromatic hydrocarbons, or a minimum plate height of about 5.5 mu m, at optimum linear velocity of ca. 2.3 mm/s and back pressure of 7.5 MPa in an acetonitrile-water (80/20, v/v) mobile phase at 40 degrees C. The permeability of the column was similar to that of a column packed with 5 mu m particles, with K-F about 2.4 x 10(-14) m(2) (based on the superficial linear velocity of the mobile phase), while the plate height value equivalent to that of a column packed with 2.5 mu m particles. Generation of 80,000-120,000 theoretical plates was feasible with back pressure below 30 MPa by employing two or three 25 cm columns connected in series. The use of the long columns enabled facile generation of large numbers of theoretical plates in comparison with conventional monolithic silica columns or particulate columns. Kinetic plot analysis indicates that the monolithic columns operated at 30 MPa can provide faster separations than a column packed with totally porous 3-mu m particles operated at 40 MPa in a range where the number of theoretical plates (N) is greater than 50,000. (C) 2010 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.chroma.2010.11.032

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

It is probably impossible to prepare high-performance liquid chromatography (HPLC) columns that have a completely homogeneous packing structure. Many reports in the literature show that the radial distributions of the mobile phase flow velocity and the local column efficiency are not flat, even in columns considered as good. A degree of radial heterogeneity seems to be a common property of all HPLC columns and an important source of peak tailing, which prevents the derivation of accurate information on chromatographic behavior from a straightforward analysis of elution peak profiles. This work reports on a numerical method developed to derive from recorded peak profiles the column efficiency at the column center, the degree of column radial heterogeneity, and the polynomial function that best represents the radial distributions of the flow velocity and the column efficiency. This numerical method was applied to two concrete examples of tailing peak profiles previously described. It was demonstrated that this numerical method is effective to estimate important parameters characterizing the radial heterogeneity of chromatographic columns.

DOI： 10.1021/ac102195x

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

A detailed analysis of a procedure of measurement of the external mass transfer coefficients (k(f)) in RPLC systems is provided. Application is described for a system consisting of a C-18-silica monolithic column and a methanol/water eluent (70/30, v/v). The k(f) values of butylbenzene at 298 K were derived from peak profiles recorded in pulse response experiments by subtracting the contributions of the kinetic processes, i.e., axial molecular diffusion, eddy diffusion, pore and surface diffusion, from the band variance. This approach provided the Sherwood number (Sh) for a range of Reynolds number (Re) between 0.002 and 0.005 and a Schmidt number (Sc) equal to 2.7 x 10(3). The experimental values of k(f) were compared with those estimated from literature correlations, giving a relative error of ca. 11% when Pfeffer equation was used for estimating k(f). The exponents obtained for Re and Sc in Sh were 0.43 and 0.39, values comparable with those found in literature correlations, i.e., 0.33. The k(f) values estimated using the reference correlations are of the same order of magnitude as the experimental k(f) values. The acquisition of more experimental data is needed for deriving an improved correlation affording more accurate estimates of k(f) in stationary phases of cylindrical shape, like silica monoliths. (C) 2010 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.ces.2010.08.020

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

The peak-parking (PP) method permits the measurement of molecular diffusivities (D(m)) in solutions. D(m) is first measured for benzene in pure methanol and acetonitrile (ACN), using an empty open tube. This yields an effective axial diffusion coefficient (D(ax,m)) equal to D(m) because there is no tortuosity nor constriction in the flow channel. The same measurements made for the same combinations of solute and solvents, using a column packed with non-porous silica particles provides the obstructive factor (Y(m)), defined as the ratio D(ax,m)/D(m), which accounts for the influence of tortuosity and constriction of the interparticulate space in packed columns on axial molecular dispersion. The value obtained for Y(m), 0.74-0.75, is constant, irrespective of the solvent. Then, PP experiments were made with the same apparatus and column to measure D(m) for benzene, toluene, and ethylbenzene in aqueous solutions of methanol and ACN. The values of D(m) obtained by correcting the experimental D(ax,m) values with Y(m) were compared with values previously reported and those estimated by several literature correlations. They were in good agreement with each other. The average relative error is estimated at 4.5-10%, demonstrating that the PP method is practically effective for experimental measurements of D(m). (C) 2010 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.ces.2010.03.027

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

External mass transfer coefficients (k(f)) were measured for a column packed with fully porous C(18)-silica spherical particles (50.6 mu m in diameter), elutecl with a methanol/water mixture (70/30,v/v). The pulse response and the peak-parking methods were used. Profiles of elution peaks of alkylbenzene homologues were recorded at flow rates between 0.2 and 2.0 mL min(-1). Peak-parking experiments were conducted under the same conditions, to measure intraparticle and pore diffusivity, and surface diffusion coefficients. Finally, the values of k(f) for these compounds at 298 K were derived from the first and second moments of the elution peaks by subtracting the contribution of intraparticle diffusion to band broadening. As a result, the Sherwood number (Sh was measured under such conditions that the Reynolds (Re) and the Schmidt numbers (Sc) varied from 0.004 to 0.05 and from 1.8 x 10(3) to 2.7 x 10(3), respectively. We found that Sh is proportional to Re(alpha) and Sc(beta) and that the correlation between these three nondimensional parameters is almost the same as those given by conventional literature equations. The values of alpha and beta were close to those in the literature correlations, between 0.26 and 0.41 and between 0.31 and 0.36, respectively. The use of the Wilson-Geankoplis equation to estimate k(f) values entails a relative error of ca. 15%. So, conventional literature correlations provide correct estimates of k(f) in HPLC systems, even for particle sizes of the order of a micrometer. (C) 2010 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.chroma.2010.02.075

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

It has been shown previously that most columns are not radially homogeneous but exhibit radial distributions of the mobile phase flow velocity and the local efficiency. Both distributions are best approximated by fourth-order polynomial, with the velocity in the column center being maximum for most packed columns and minimum for monolithic columns. These distributions may be an important source of tailing of elution peaks. The numerical calculation of elution peaks shows how peak tailing is related to the characteristics of these two distributions. An approach is proposed that permits estimations of the true efficiency and of the degree of column radial heterogeneity by inversing this calculation and using the tailing profiles of the elution peaks that are experimentally measured. This method was applied in two concrete cases of tailing peak profiles that had been previously reported and were analyzed by applying this new inverse approach. The results obtained prove its validity and demonstrate that this numerical method is effective for deriving the true column efficiency from experimental tailing profiles. (C) 2009 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.chroma.2009.09.006

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS INC  

A peak parking-moment analysis method was used for the measurement of surface diffusion coefficient (D-s) in a reversed-phase liquid chromatography (RPLC) system consisting of a C-18-silica monolithic column and a mixture of methanol and water (70/30, v/v). The D-s values experimentally measured were analyzed by considering the correlation with corresponding values of molecular diffusivity (D-m) and the retention equilibrium constant (K-a). It seems that the correlation between D-s/D-m and K-a is represented by a single curve irrespective of the RPLC conditions of temperature and the type of sample compounds. The increase in K-a is accompanied with the decrease in D-s/D-m. Oppositely, the ratio of D-s/D-m increases and approaches around unity when K-a infinitely decreases. It seems that surface diffusion is originally similar to molecular diffusion and that it is restricted due to the sample retention. These characteristics of surface diffusion are the same between the C-18-silica monolithic stationary phase and the conventional C-18-silica gel particles. In addition, the values of K-a and D-s are also comparable between them. It is concluded that basic properties concerning the retention equilibrium and surface diffusion of the C-18-silica monolithic stationary phase are almost the same as those of the conventional C-18-silica gel particles in spite of the difference between their structural characteristics.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

The combination of series of measurements of band broadening made with the peak parking (PP) method, using successively an open capillary tube and a HPLC column, gives a convenient procedure for the measurement of the molecular diffusivity (D(m)) of compounds in solutions, of their axial dispersion coefficient (D(ax,m)) in chromatographic columns, and of the tortuosity or obstructive factor of the column bed. The molecular cliffusivity measured for benzene in methanol was in excellent agreement with literature data. The ratio of the axial dispersion coefficient to this diffusivity gives the obstructive factor (gamma(m)) of the packed bed. which was 0.74 for the column used. The values of D(m) in other solutions were obtained from the D(ax,m) values measured by the PP method, by correcting the D(ax,m) values with the gamma(m) value. The D(m) values determined by this method were in good agreement with those previously reported or estimated using literature correlations. These results showed that the PP method is effective for the experimental measurement of D(m). (C) 2009 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.chroma.2009.02.058

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC ANALYTICAL CHEMISTRY  

The peak parking (PP)-moment analysis (MA) method was applied to the measurement of surface diffusion coefficients (D(s)) in reversed-phase liquid chromatography using a C(18)-silica gel and an aqueous solution of methanol (70 vol%). The values of D(s) measured by the PP-MA method were in agreement with those obtained by the pulse response (PR)-MA method, which is one of powerful strategies for the quantitative study on the mass transfer kinetics in columns and stationary phases. It was demonstrated that the PP-MA method is an alternative for the experimental measurement of D(s). The mechanism of surface diffusion was considered on the basis of molecular diffusion by introducing a restriction energy (E(r)) for surface diffusion. Physical meanings of E(r) were discussed by analyzing the correlation between the enthalpy change due to sample retention (Q(st)) and D(s). It seems that surface diffusion of a sample molecule is restricted by its retention strength and by the solvent structure formation due to the hydrophobic solvation of the stationary phase surface.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC ANALYTICAL CHEMISTRY  

A new model was developed for explaining the retention behavior in reversed-phase liquid chromatography (RPLC) on the basis of two extrathermodynamic relationships, i.e., enthalpy-entropy compensation (EEC) and linear free energy relationship (LFER). Krug's four tests were used for analyzing the temperature dependence of the retention equilibrium constant normalized by alkyl ligand density. It was demonstrated that a real EEC takes place in the retention equilibrium. A new model based on the real EEC was developed to explain the LFER concerning the retention equilibrium. The model formulates the slope and intercept of the LFER with the compensation temperatures and molecular thermodynamic parameters relating to the changes in enthalpy and entropy. The values of the retention equilibrium constant under different RPLC conditions were estimated with a relative error of 6.9%. The new model provides an alternative approach for interpreting the retention equilibrium in RPLC from the viewpoints of thermodynamics and extrathermodynamics.

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Language：English   Publishing type：Research paper (scientific journal)  

A new model was developed for explaining the retention behavior in reversed-phase liquid chromatography (RPLC) on the basis of two extrathermodynamic relationships, i.e., enthalpy-entropy compensation (EEC) and linear free energy relationship (LFER). Krug's four tests were used for analyzing the temperature dependence of the retention equilibrium constant normalized by alkyl ligand density. It was demonstrated that a real EEC takes place in the retention equilibrium. A new model based on the real EEC was developed to explain the LFER concerning the retention equilibrium. The model formulates the slope and intercept of the LFER with the compensation temperatures and molecular thermodynamic parameters relating to the changes in enthalpy and entropy. The values of the retention equilibrium constant under different RPLC conditions were estimated with a relative error of 6.9%. The new model provides an alternative approach for interpreting the retention equilibrium in RPLC from the viewpoints of thermodynamics and extrathermodynamics. © 2009 The Japan Society for Analytical Chemistry.

DOI： 10.2116/analsci.25.219

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

External mass transfer in a HPLC system operated in the reversed-phase mode was studied by pulse response experiments, using a column packed with non-porous C-18-silica gel spherical particles. 18 pm in diameter. The first and second moments of the elution peaks, measured under different flow velocities and temperatures, were analyzed by the moment method to determine the external mass transfer coefficient (k(f)). The dependence of the Sherwood number on the Reynolds and the Schmidt numbers is almost the same as that observed in previous investigations of conventional literature correlations. The exponent of the last two nondimensional parameters was derived as being in the range from 0.28 to 0.41. When the Kataoka equation is used, the mean square deviation was calculated to be 0.21 for the values of kf estimated in this study. It is concluded that conventional correlations can be used to estimate kf values, even when the particle diameter is of the order of a micrometer. (c) 2008 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.chroma.2008.09.035

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Influence of column temperature and mobile phase composition (phi) on surface diffusion was studied in reversed-phase liquid chromatography using a C(18)-silica gel column and methanol-water mixtures. The temperature dependence of surface diffusion coefficient (Ds) was explained by considering that of the molecular diffusivity, suggesting the presence of a kind of correlation between surface and molecular diffusions. The influence of phi on D(s) was accounted for by considering the restriction energy (E(r)) for surface diffusion. Physical meanings of the linear correlation between E(r) and the enthalpy change due to sample retention are discussed in connection with the mechanism of surface diffusion. (c) 2008 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.chroma.2008.04.054

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Chromatographic performance of various separation media having different structural characteristics as the stationary phase for fast HPLC was quantitatively evaluated by using the new moment equations recently developed with considering the shape and porous structure of the packing materials. Four types of separation media, i.e., full-porous, partially porous (pellicular or shell) type, and non-porous spherical particles and full-porous cylindrical fiber, were chosen as examples. The moment equations were used for predicting the chromatographic behaviors of benzene under hypothetical RPLC conditions. The overall performance of the four types of packing materials as the separation media for fast HPLC was compared with each other from the viewpoint of the peak capacity, which depends on both the retention equilibrium and the mass transfer kinetics. It seems that the full-porous cylindrical fiber and the pellicular type spherical particle are more preferable than the others, i.e., the full-porous and non-porous spherical particles. Now we can use the new moment equations for the quantitative prediction of the chromatographic behaviors of the various packing materials on the basis of a related experimental information and for the evaluation of their performance from various chromatographic points of view. The new moment equations are effective not only for the detailed analyses of chromatographic behaviors but also for the preliminarily evaluation of new types of separation media for fast HPLC. (C) 2008 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.chroma.2007.12.064

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

New moment equations were systematically developed for chromatography using various types of separation media having different structural characteristics, i.e., shape (spherical particle, cylindrical fiber, flat plate) and porous structure (full-porous, partially porous (pellicular), nonporous). First, a set of basic equations of the general rate model of chromatography representing the mass balance and the mass-transfer kinetics were analytically solved in the Laplace domain. Then, the moment equations in the real-time domain of the first absolute moment and the second central moment were derived from the analytical solution in the Laplace domain. The new moment equations were used for predicting the chromatographic behaviors of benzene in the hypothetical RPLC systems using the full-porous, partially porous (pellicular), and nonporous spherical particles as packing materials. The influence of the difference in their structure on the total performance of the three types of spherical particles as the separation media for the fast HPLC with a high efficiency was quantitatively evaluated from the viewpoints of the column efficiency, column back pressure, and sample retention strength. The framework of the new moment equations can provide not only the qualitative but also the quantitative information about the intrinsic characteristics of the chromatographic behaviors of various separation media having the different shapes and structures. This study is devoted to demonstrating the important advantage of the moment analysis strategy over the conventional plate theory and rate models of chromatography.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Surface diffusion phenomena were studied from kinetic and thermodynamic points of view. The existence of a linear free energy relationship between surface diffusion and the retention equilibrium suggests that the mechanism of surface diffusion is the same irrespective of the density of C-1 and C-18 ligands. Surface diffusion coefficient (D-s) of weakly retained compounds seems to be of the same order of magnitude with corresponding molecular diffusivity. There would be an intimate correlation between surface diffusion and molecular diffusion. The value of D, decreases with increasing retention strength. The magnitude of the restriction for surface diffusion is comparable to about one third the enthalpy change due to the sample retention. This means that it is necessary for sample molecules adsorbed to be partially desorbed from the stationary phase surface when they migrate by surface diffusion. The results of this study provide the fundamental information for developing an appropriate model of surface diffusion, which explains some intrinsic characteristics and mechanism of surface diffusion. (C) 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.chroma.2007.08.045

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

The combination of peak parking and moment analysis is proved to be a powerful strategy for studying the molecular diffusivity of solute molecules in stationary phases and for determining the corresponding kinetic parameters. The physical meaning of the traditional kinetic parameter, gamma D-s(s), the diffusion coefficient of solute molecules in stationary phases, is first clarified. A second kinetic parameter, D-Ls, is then derived from gamma D-s(s), and the correspondence between D-Ls and the surface diffusion coefficient, D-sur, is discussed. Then, the results of peak parking experiments carried out with RPLC systems using aqueous methanol solutions and C-18-silica columns are reported. The moments of pulse responses were measured and are analyzed. The values and some characteristics of D-Ls measured by the peak parking-moment analysis method are compared with those of D-sur determined using the pulse response-moment analysis method. The comparison of the numerical values of D-Ls and D-sur suggests that D-Ls is nearly equal to D-sur and that it exhibits the same dependence on the retention strength as does D-sur with regard to the mass-transfer kinetics and extrathermodynamics. This comparison allows us to conclude that D-Ls corresponds to D-sur. The advantages and disadvantages of the peak parking-moment analysis method were compared with those of the pulse response-moment analysis method. The combination of these two methods provides a comprehensive strategy for measuring the mass-transfer kinetics in the stationary phase.

DOI： 10.1021/ac061321h

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Surface diffusion in reversed-phase liquid chromatography (RPLC) using silica gels bonded with C-1 and C-18 alkyl ligands of different densities was studied from the viewpoints of two extrathermodynamic relationships, i.e., enthalpy-entropy compensation (EEC) and linear free energy relationship (LFER). First, according to the four methods proposed by Krug et al., the values of surface diffusion coefficient (D-s) were analyzed to confirm that an actual EEC resulting from substantial physico-chemical effects takes place for surface diffusion. Then, it was also demonstrated that a LFER is observed between surface diffusion and the retention equilibrium. The establishment of EEC and LFER suggests a mechanistic similarity of molecular migration by surface diffusion, irrespective of the alkyl chain length and the densities of C-1 and C-18 ligands. Finally, a thermodynamic model for the LFER based on the real EEC was used to estimate D-s values under various RPLC conditions. The D-s values can be estimated with a mean square deviation of about 25-30%. The agreement between the D-s values estimated and those experimentally measured suggests that the total mass flux by surface diffusion consists of the two contributions due to C-1 and C(1)8 ligands and that the contribution of each ligand is proportional to the ligand density. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.talanta.2006.08.020

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

Mass transfer in monolithic C-18-silica stationary phases and C-18-silica gel particles was studied. A traditional kinetic parameter, gamma D-s(s), which is a diffusion coefficient of solute molecules in the stationary phase, was measured by two unusual approaches, i.e., peak-parking and slow-elution methods. The correlation between the ratio of y(s)D(s) to molecular diffusivity (D-m) and the retention factor (k) was represented by one common curve, irrespective of the RPLC conditions. A similar curved profile was also observed between another kinetic parameter (D-Ls), which is related to the axial diffusive molecular migration in the stationary phase, and the retention equilibrium constant (K-a). The values of D-Ls and K-a were calculated from those of gamma D-s(s) and k, respectively. The ratio of D-Ls/D-m increases with decreasing K-a and seems to approach around unity when Ka is infinitely small. The dependence of DL, on Ka was also studied from extra-thermodynamic points of view. The linear correlation between ln D-Ls and In Ka suggests the existence of a kind of linear free energy relationship between the mass transfer in the stationary phase and the retention equilibrium. Because these characteristics of DLs are similar to those of the surface diffusion coefficient (D-sur) D-Ls seems to correspond to D-sur.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

The contribution of molecular diffusion to peak broadening was studied in a reversed-phase HPLC system, consisting of a monolithic silica C Is column and methanol-water mobile phase. Study on the band broadening effect of holding a solute in a column or elution at very low linear velocity of mobile phase allowed facile determination of the contribution of the molecular diffusion term. Less obstruction against molecular diffusion, or the faster axial band dispersion in a monolithic silica column than in a particle-packed column, was found both in mobile phase and in stationary phase. (c) 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.chroma.2005.11.053

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

The retention behavior on silica gels bonded to C-18 and C-1 alkyl ligands of different densities was studied in reversed-phase liquid chromatography (RPLC) from the viewpoints of two extrathermodynamic relationships, enthalpy-entropy compensation (EEC) and linear free energy relationship (LFER). First, the four tests proposed by Krug et al. were applied to the values of the retention equilibrium constants (K) normalized by the alkyl ligand density. These tests showed that a real EEC of the retention equilibrium originates from substantial physico-chemical effects. Second, we derived a new model based on the EEC to explain the LFER between the retention equilibria under different RPLC conditions. The new model indicates how the slope and intercept of the LFER are correlated to the compensation temperatures derived from the EEC analyses and to several parameters characterizing the molecular contributions to the changes in enthalpy and entropy. Finally, we calculated K under various RPLC conditions from only one original experimental K datum by assuming that the contributions of the C-18 and C-1 ligands to K are additive and that their contributions are proportional to the density of each ligand. The estimated K values are in agreement with the corresponding experimental data, demonstrating that our model is useful to explain the variations of K due to changes in the RPLC conditions. (c) 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.chroma.2005.09.001

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC ANALYTICAL CHEMISTRY  

The performance of an open-tubular capillary column coated with a modified silica-gel thin layer was investigated, particularly concerning the effect of the silanization process on it. Although the increase in the octadecyltriethoxysilane (ODTES) concentration in the silanization process could enhance the retention factor of naphthalene, its theoretical plate number was significantly reduced (ODTES, 5 to 50%; k, 0.2 to 4.3; N, 79600 to 2600 m(-1)). Namely, the increase in the retention factor was accompanied by a decrease in the theoretical plate number. A similar phenomenon was also observed when octadecyldimethylchlorosilane (ODCS) was used as the silanization regent. However, increases in both the retention factor and the theoretical plate number could be achieved (sample, naphthalene; k, 0.05 to 0.09; N, 149000 to 220000 m-1) by a NaOH treatment to the fabricated thin porous silica-get layer before silanization with ODCS. The electrochromatographic separation of proteins and peptides by using the NaOH-treated column could obtain more peaks than electrophoretic separation.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Surface diffusion on adsorbents made of silica gels bonded to C-1, C-4, C-8, and C-18 alkyl ligands was studied in reversed-phase liquid chromatography (RPLC) from the viewpoints of two extrathermodynamic relationships: enthalpy-entropy compensation (EEC) and linear free-energy relationship (LFER). First, the values of the surface diffusion coefficient (D-s), normalized by the density of the alkyl ligands, were analyzed with the modified Arrhenius equation, following the four approaches proposed in earlier research. This showed that an actual EEC resulting from substantial physicochemical effects occurs for surface diffusion and suggested a mechanistic similarity of molecular migration by surface diffusion, irrespective of the alkyl chain length. Second, a new model based on EEC was derived to explain the LFER between the logarithms of D-s measured under different RPLC conditions. This showed that the changes of free energy, enthalpy, and entropy of surface diffusion are linearly correlated with the carbon number in the alkyl ligands of the bonded phases and that the contribution of the C-18 ligand to the changes of the thermodynamic parameters corresponds to that of the C-10 ligand. The new LFER model correlates the slope and intercept of the LFER to the compensation temperatures derived from the EEC analyses and to several parameters characterizing the molecular contributions to the changes in enthalpy and entropy. Finally, the new model was used to estimate D-s under various RPLC conditions. The values of D-s that were estimated from only two original experimental D-s data were in agreement with corresponding experimental D-s values, with relative errors of similar to 20%, irrespective of some RPLC conditions.

DOI： 10.1021/jp058028q

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC ANALYTICAL CHEMISTRY  

A new type of fiber adsorbent attached with silica microparticles was prepared. The silica microparticles were formed by the polymerization of silica oligomers on glass fibers, which were woven into a glass filter. The surface of the silica microparticles was chemically modified by bonding C(18)-ligands. SEM images indicated that the diameter of the uniform and spherical silica microparticles fixed on glass fibers was on the order of micrometers. It was confirmed that the glass filter adsorbent was effective for the adsorptive removal of toluene of low concentrations.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Four parameters characterizing the adsorption equilibrium, surface diffusion, and related thermodynamic properties were derived from pulse-response experiments in various reversed-phase liquid chromatography (RPLC) systems using C-18-silica gels and aqueous solutions of three different organic modifiers, methanol, acetonitrile, and tetrahydrofuran. The results were compared with corresponding data similarly measured by gas-solid chromatography on the same type of surface-modified silica gel, with helium. Information on the solvent effect on the adsorption characteristics was provided by the comparison of these experimental results. While the adsorption equilibrium constant and the heat of adsorption at infinite dilution were much larger in the gas-solid than in the RPLC system, the surface diffusion coefficient (D-s) and the activation energy of surface diffusion (E-s) were of the same order of magnitude in both systems. Regarding surface diffusion, the logarithm of the frequency factor was linearly correlated with E-s by the same straight line, suggesting the fundamental similarity of the surface diffusion mechanism in the gas-solid and liquid-solid systems. Calculations made on the basis of a surface-restricted diffusion model provide an explanation for the comparable values of D-s and E-s in the two systems. In conclusion, the liquid phase in RPLC influences the thermodynamic parameters of surface diffusion as well as those of adsorption equilibrium, but similar values of D-s and E-s are observed in both the two adsorption systems. A quantitative explanation of the similarities and differences of the characteristics and the mechanism of surface diffusion in gas-solid and liquid-solid adsorption systems is proposed.

DOI： 10.1021/jp0309421

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

The moment analysis of elution peak profiles based on new moment equations provides information on the mass-transfer characteristics of C-18-silica monolithic columns. The flow rate dependence of the HETP data was analyzed using the generalized van Deemter equation, after correction of these data by subtraction of the external mass-transfer contribution to band broadening. Kinetic parameters and diffusion coefficients related to the mass-transfer processes in monolithic columns were derived by taking advantage of the different flow velocity dependence of their contributions to band broadening. At high flow rates, axial dispersion and diffusive migration across the monolithic C-18-silica skeleton contribute much to band broadening, suggesting that it remains important to reduce the influence of eddy diffusion and the mass-transfer resistance in the stationary phase to achieve fast separations and a high efficiency. Surface diffusion plays a predominant role for molecular migration in the monolithic stationary phase. Although the value of the surface diffusion coefficient (D-s) depends on an estimate of the external mass-transfer coefficient, D-s values of the order of 10(-7) cm(2) s(-1) were calculated for the first time for the C-18-silica monolithic skeleton. The value of D-s decreases with increasing retention of sample compounds. Analysis of a kind of time constant calculated from Ds suggests that the "chromatographic corresponding particle size" is similar to4 mum for the C-18-silica monolithic stationary phase used in this study. The accuracy of the D-s values determined was discussed.

DOI： 10.1021/ac0302206

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WATER ENVIRONMENT FEDERATION  

Column experiments were used to measure the hydrodechlormation rate of relatively high concentrations of trichloroethene (TCE) (approximately 100 mg L-1). Trichloroethene in water was treated with a platinum on titania (Pt-TiO2) catalyst and hydrazine. The influence of some experimental conditions (i.e., flowrate, temperature, and pH) on the catalytic conversion of TCE was studied. The pseudo-first-order rate constant of the overall hydrodechlorination of TCE was approximately I X 10(-3) to 1 x 10(-2) s(-1) in the temperature range of 283 to 328 K and was determined from the dependence of the TCE conversion on the contact time of the feed water with the catalyst by assuming first-order kinetics. The activation energy of the catalytic hydrodechlorination of TCE was calculated as approximately 34 kJ/mol from the temperature dependence of the rate constant. The TCE conversion increases with increasing pH, and probably correlates with the presence of un-ionized hydrazine.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

Information about retention equilibrium, mass transfer kinetics, and related thermodynamic properties of chromatography using phenyldimethylsilyl (Ph)-silica gel was derived by moment analysis of pulse response peak profiles. The results for the Ph-silica gel were compared with those for octadecyldimethylsilyl (C-18)-silica gel. Some parameters characterizing the chromatographic behavior of the two stationary phases were correlated with the hydrophobic surface area of sample molecules. Surface diffusion had a predominant role for intraparticle diffusion. An enthalpy-entropy compensation was established for both the retention equilibrium and surface diffusion. A linear correlation was observed between the logarithm of surface diffusion coefficient (D-s) and that of retention equilibrium constant (K-a), suggesting the establishment of a linear free energy relationship. The ratio of D-s to molecular diffusivity (D-m) decreased with increasing K-a and was correlated by a single curved line. The value of D-s was of the same order of magnitude with D-m when K-a became negligible. These results suggest the presence of a sort of correlation between surface diffusion and molecular diffusion and the restriction of the molecular mobility by surface diffusion due to the retention strength.

DOI： 10.1039/b308293h

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

The fundamentals of the retention equilibrium in reversed-phase liquid chromatography (RPLC) are studied on the basis of enthalpy-entropy compensation (EEC). First, retention data were acquired and the influence of the nature of the compounds, organic solvent modifier, and temperature on these data was assessed. Then, the data were analyzed according to the four different methods proposed by Krug et al., and an EEC was formally established. Linear correlations were observed between the logarithm of the adsorption equilibrium constants under the different RPLC conditions, suggesting linear free energy relationships (LFERs). Finally, the variations of the retentions with the experimental conditions are shown to be quantitatively explained by a new model based on EEC. Ibis model affords a comprehensive interpretation of the variations of retention originating from changes of either one parameter alone or several simultaneously. The slope and intercept of the LFER that relates two equilibrium systems are accounted for by the new model. The parameters of this model are the changes of enthalpy and entropy associated with the retention, the compensation temperatures, and the experimental conditions.

DOI： 10.1021/ac0202233

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Enthalpy- entropy compensation (EEC) and linear free energy relationships (LFER) are extrathermodynamic correlations frequently used to discuss the mechanistic similarities of chemical equilibria and reaction kinetics. Although empirical, they are widely applied, proving the substantial effectiveness of fundamental studies based on them. Many attempts have been made to interpret theoretically the necessary conditions (or preconditions) of EEC and LFER. LFER is known to rest on the existence of EEC. However, the intimate correlations between EEC on one hand and LFER and the temperature dependence of LFER on the other hand were insufficiently discussed from the viewpoint of molecular structure contributions. We present a simple LFER model relating the slope and intercept of LFER to the compensation temperatures, themselves derived from EEC analyses, and to several parameters characterizing the molecular contributions to the changes in enthalpy and entropy associated with the passage from one phase of the chromatographic system to the other. A theoretical explanation is supplied for the intimate correlation between the two types of extrathermodynamic relationships, EEC and LFER. We demonstrate also that the characteristics of EEC and LFER depend on the structural parameters. This new model allows a proper interpretation of the temperature dependence of LFER. It should permit further progress of fundamental studies of chemical reaction mechanisms based on extrathermodynamic relationships.

DOI： 10.1021/ac020245p

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

The solution in the Laplace domain of the system of equations of the general kinetic model of chromatography provides equations relating the first absolute moment and the second central moment of elution bands to the characteristics of the retention equilibrium and the mass transfer kinetics, respectively. For continuous porous rod (i.e., monolithic) columns, these moment equations have the same form as those for conventional columns packed with. spherical particles of a suitable packing material. However, some of the coefficients in the equation of the second central moment are different for conventional and monolithic columns. The results of the calculations made with the moment equations derived here for monolithic columns agree well with some typical characteristics of the experimental behavior observed for monolithic columns, showing the validity of these new moment equations. They should be useful for a detailed analysis of the retention equilibrium and of the mass transfer kinetics in monolithic-type columns. These moment equations are also applicable to the study of the adsorption characteristics of cylindrical adsorbents, such as activated carbon fibers.

DOI： 10.1021/jp020555b

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

A new model of surface diffusion in reversed-phase liquid chromatography (RPLC) was derived by assuming a correlation between surface and molecular diffusion. Analysis of surface diffusion data under different conditions of sample compounds, mobile and stationary phases, and temperature in RPLC systems validates this assumption and shows that surface diffusion should be regarded as a molecular diffusion restricted by the adsorptive interactions between the adsorbate molecule and the stationary phase surface. A surface-restricted molecular diffusion model was proposed as a first approximation for the mechanism of surface diffusion. The model is formulated according to the absolute rate theory. The activation energy of surface diffusion (E-s) was quantitatively interpreted assuming that E-s consists of the contributions of two processes, a hole-making and a jumping one. The former contribution is nearly equal to the activation energy of molecular diffusion and is correlated with the evaporative energy of the mobile phase solvent. The latter contribution is a fraction of the isosteric heat of adsorption. An appropriate explanation based on this new model of surface diffusion is provided for two contradictory results related to the relationship between retention equilibrium and surface diffusion in RPLC and to the surface diffusion coefficient for weakly retained sample compounds. (C) 2002 Elsevier Science BV All rights reserved.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Kinetic and thermodynamic parameters concerning surface diffusion were derived in reversed-phase liquid chromatography (RPLC) systems using a series of silica gel packing materials bonded with C-1, C-4, C-8, and C-18 alkyl ligands. In this paper, a more detailed study on some characteristics and the mechanism of surface diffusion in the RPLC systems using the different alkyl ligand bonded silica gels was made from a thermodynamic point of view by analyzing the surface diffusion data with consideration of the correlation between the parameters concerning surface diffusion and those relating to the retention equilibrium. The mechanism of surface diffusion seems to be the same irrespective of the length of the alkyl ligands because of the presence of the extrathermodynamic relationships, i.e., the enthalpy-entropy compensation and the linear free energy relationship. It was indicated that the surface diffusion coefficient (D-s) of weakly retained compounds was of the same order of magnitude with corresponding molecular diffusivity and that D-s decreased with increasing retention. The activation energy of surface diffusion (E-s) was formulated as a linear function of the isosteric heat of adsorption (Q(st)). A modified Arrhenius equation, which is derived by taking into account the linear correlation between the two thermodynamic parameters E-s and Q(st), appropriately explains the intrinsic characteristics and mechanism of surface diffusion.

DOI： 10.1021/ac011184i

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Language：English   Publishing type：Research paper (international conference proceedings)  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

Pulse response experiments (i.e., elution chromatography) were made in reversed-phase liquid chromatography (RPLC) using a C-18 silica gel column and methanol-water mixtures of different compositions (phi). The moment analysis of the elution peak profiles measured in the RPLC system provided some items of information about four parameters characterizing the retention equilibrium and the mass transfer kinetics in the column, i.e., adsorption equilibrium constant, isosteric heat of adsorption, surface diffusion coefficient and activation energy of surface diffusion. Characteristics of the chromatographic behavior were studied by analyzing the dependence of the four parameters on phi and the correlation between them. It was found that surface diffusion was one of the important processes of molecular migration having a significant contribution to the mass transfer kinetics in the column. Both the adsorption equilibrium constant and the surface diffusion coefficient varied depending on phi. The direction of their changes was approximately opposite, suggesting that the mass transfer in the manner of surface diffusion was restricted owing to the retention of the sample molecules on the stationary phase.

DOI： 10.1039/b203667n

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Language：English   Publishing type：Research paper (scientific journal)  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Surface diffusion data previously measured for different compounds, mobile phase solvents, stationary phases, and temperatures in reversed-phase liquid chromatography (RPLC) were reevaluated to derive information related to the mechanism and characteristic features of surface diffusion. First, a comparison of the surface diffusion coefficient (D-s) and the corresponding molecular diffusivity (D-m) suggests that the dependence of D-s on the RPLC conditions is a consequence of that of D-m. There is a correlation between surface diffusion coefficients and molecular diffusivity. Second, we showed that D-s correlates with the adsorption equilibrium constant (K) and the isosteric heat of adsorption (Q(st)). These two parameters represent the intensity of the adsorptive interactions between the sample molecules and the surface of the stationary phase. Finally, the ratio Ds/Dm increases with decreasing K and -Q(st) and D-s becomes of the same order of magnitude as D-m when the adsorptive interactions become small. These results imply that surface diffusion should be regarded as molecular diffusion restricted by the influence of adsorptive interactions. Other information on surface diffusion was also obtained. The value of D,. extrapolated at Q(st) = 0 is not equal to D-s The difference between the two coefficients depends on the experimental conditions, e.g., the nature of the organic modifier in the mobile phase or the surface density of the C-18 alkyl ligand on the stationary phase. Our results demonstrate that surface diffusion is fundamentally related to molecular diffusion.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Surface diffusion of alkylbenzene and p-alkylphenol derivatives was measured in reversed-phase liquid chromatography on a C-18-silica column with a methanol/water mixture (70/30, v/v) as the mobile phase. They were analyzed on the basis of the restricted molecular diffusion model for surface diffusion, The temperature dependence of the surface diffusion coefficient (D-s) arises probably from that of molecular diffusivity, suggesting a correlation between surface and molecular diffusion. Other correlations were also observed: (1) an enthalpy-entropy compensation of the retention equilibrium constant, (2) a linear free energy relationship between the retention and surface diffusion, and (3) a linear correlation between the restriction energy of surface diffusion and the isosteric heat of adsorption, The physical meaning of parameters involved in the surface-restricted molecular diffusion model is discussed on the basis of these results. A practical and convenient procedure for the estimation of D-s is also suggested. This study demonstrates how surface diffusion phenomena can be accounted for on the basis of the correlation between surface and molecular diffusion.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

The characteristics of the retention and the mass transfer kinetics in reversed-phase liquid chromatography (RPLC) were measured on a system consisting of a C-18-silica gel and a tetrahydrofuran-water (50:50, v/v) solution. These parameters were derived from the first and the second moments of the elution peaks, respectively. Further information on the thermodynamic properties of this system was derived from the temperature dependence of these moments. Some correlations previously established were confirmed for this system, namely, an enthalpy-entropy. compensation for both retention and surface diffusion and a linear free-energy relationship. These results are compared with those observed in other similar systems using methanol-water (70:30, v/v) and acetonitrile-water (70:30, v/v) solutions. The contribution of surface diffusion to intraparticle diffusion in C-18-silica gel particles was shown to be important. The analysis of the thermodynamic properties of surface diffusion suggests that, in these three RPLC systems, its activation energy is lower than the isosteric heat of adsorption. The nature and the extent of the influence of the mobile phase composition on the parameters describing the retention and the mass transfer kinetics are different but the chromatographic mechanisms involved in RPLC systems appear similar, irrespective of the nature of the organic modifier in the mobile phase. (C) 2001 Elsevier Science B.V. All rights reserved.

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Society of Polymer Science, Japan  

Biodegradation behavior of test pieces of some biodegradable polymers formed by injection molding was investigated in soil, aqueous environments, and an activated sludge. The manner of the biodegradation depended on the composition of materials. With regard to the tests in soil and aqueous environments in the field, the degradation progressed during spring and fall. In an activated sludge of a sewage treatment plant, Biopol and Mater-Bi were degraded. The extent of the degradation of Biopol was influenced by the density of microbes. The degradation of Biopol was facilitated in an aeration tank, in which the microbe density was high. It was estimated that about 50 wt% of the biodegradable polymers was degraded in one year in the activated sludge. Waste treatment of polymers in a sewage treatment plant would be one of the effective methods, provided the safety of the treatment is confirmed.

DOI： 10.1295/koron.58.59

CiNii Article

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

The parameters characterizing retention and the mass transfer mechanisms in reversed-phase liquid chromatography were derived from data acquired for a series of compounds on a silica gel bonded to alkyl ligands of various lengths and Ligand densities. The adsorption equilibrium constant, the absolute value of the isosteric heat of adsorption, and the activation energy of surface diffusion increase while the surface diffusion coefficient decreases with increasing length of the alkyl chain and density of the C-18 ligand. These results are consistent with increasing restriction of the mobility of an increasingly adsorbable molecule. There is a critical level of carbon content above which the four parameters just listed no longer change with increasing alkyl ligand density. This level is likely to depend on the sizes of the alkyl ligand and the sample molecule. Even at high densities of C-18 chains, there may be a limitation in the contact area of the sample molecule and the alkyl ligand, The retention behavior on the stationary phases studied is explained by assuming that the sample molecules penetrate into the layer of alkyl ligands. Enthalpy-entropy compensation was demonstrated for surface diffusion. Its mechanism is probably similar on the different stationary phases studied, irrespective of the length and density of the bonded ligand. (C) 2000 Elsevier Science B.V. All rights reserved.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

The characteristic features of mass-transfer kinetics in a reversed-phase (RP) column packed with a C18-silica were studied. The relevant information on phase equilibrium thermodynamics and mass-transfer kinetics was obtained by frontal analysis and the pulse method, respectively. The equilibrium isotherm was accounted for by the simple Langmuir model. The ratio of the axial dispersion coefficient to the mobile-phase now velocity increased almost linearly with increasing solute concentration. Similarly, the mass-transfer rate coefficient (k(m)) showed a linear dependence on the solute concentration. The positive concentration dependence of k(m) resulted from that of the surface diffusion coefficient, which was interpreted with the chemical potential driving force model. The contribution of axial dispersion to band broadening was predominant in the RP column packed with the medium-size packing material used (particle diameter, 12 mum) whereas that of the kinetics of adsorption/desorption was negligibly small, The results of this study demonstrate how an analysis of the dependence of the mass-transfer kinetics on the flow velocity and the solute concentration allows a better understanding of this kinetics.

DOI： 10.1021/ac0002801

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

A theoretical basis was given for the linear additive representation of the logarithm of ion-pair solvent extraction constant (K-ex) in terms of logarithmic values of three individual extraction constants (K-cation, K-anion, and K-solvent) for cations, anions, and organic solvents constituting ion-pair extraction systems. The differences in extractability between cations and between anions were quantitatively discussed according to the thermodynamic cycle model of 1:1 ion-pair extraction. The increment of log K-cation and log K-anion of hydrophobic ions is explained by taking the increment of the free energy change of the hydration (Delta G(hyd)) Of the ions into account. The order of the extractability of inorganic cations and anions was also interpreted using literature data of Delta G(hyd) of each inorganic ion. The free energy change of the solvation of a hypothetical ion-pair having a shape of spherical was calculated on the basis of the solvophobic theory. The difference in extracting powers of some extracting organic solvents could also quantitatively be interpreted. There are a few sets of proposed values of the individual extraction constants representing the extractability of the cations and anions, which were calculated based on different reference assumptions. The conclusions of this study an effective for the interpretation concerning the increment of the extractability of the ions irrespective of the reference assumptions for determining the individual extraction constants. It was also attempted to estimate absolute values of K-ex by the theoretical approach in this study. The K-ex values of a few inorganic ion-pairs thus calculated were of the same order of magnitude as those estimated from the individual extraction constants experimentally determined. It is concluded that the thermodynamic cycle model based on the solvophobic theory provides an essential framework for the theoretical interpretation of the mechanism of the ion-pair extraction, and that the validity of the linear additive representation of log K-ex with the three individual extraction constants is demonstrated.

DOI： 10.1021/jp000918c

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

The influence of the column radial heterogeneity on the determination of equilibrium isotherm data by the elution by characteristic point (ECP) method is studied using nondimensional numerical calculations and taking into account typical radial distributions of the mobile phase flow velocity and the column efficiency across a column. Overloaded elution peaks were calculated with the equilibrium-dispersive model as a function of four dimensionless parameters, the number of theoretical plates at the center of the column, the Langmuir equilibrium constant, the retention and the loading factors. The influence of the mass transfer resistances and the radial heterogeneity of the column on the ECP data was analyzed by comparing the true isotherm and the one estimated from the diffuse profile of overloaded peaks. The results provide information on the accuracy of the ECP method. The error made increases with increasing degree of radial heterogeneity. This error can be corrected by using the results of the nondimensional numerical calculations, allowing a further extension of the applicability of the ECP method. (C) 2000 Elsevier Science B.V. All rights reserved.

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Language：English   Publishing type：Research paper (scientific journal)  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

The validity of measurements of the lumped mass transfer rate coefficient (k(m,L)) is studied on the basis of experimental data acquired under Langmuir isotherm conditions, in reversed-phase liquid chromatography. Two different methods were used, the perturbation method and frontal analysis. Accurate values of k(m,L) can be properly obtained by the perturbation method because, with this method, the chromatographic processes take place under locally linear isotherm conditions. Values of k(m,L) can also be derived from the breakthrough curves obtained in frontal analysis. Because the contribution of axial dispersion to band broadening was larger than that of the mass transfer resistances, the apparent axial dispersion coefficient (D-a) was first derived from the breakthrough curve by applying the equilibrium-dispersive model. Then, the value of k(m,L) was calculated from D-a. The values of k(m,L) determined by the two methods were in close agreement in the range of nondimensional Langmuir equilibrium constants (r = 1/[1+KLC0]) between 0.32 and 0.85, irrespective of the mobile phase flow velocity. Thus, frontal analysis can be used for kinetic studies of the mass transfer in chromatographic columns. (C) 2000 Elsevier Science B.V. All rights reserved.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC ANALYTICAL CHEMISTRY  

Kinetic data previously acquired on the enantiomeric separation of L- and D-phenylalanine anilide (PA) on a polymeric stationary phase imprinted with L-PA were reinterpreted. The parameters characterizing the mass transport processes active in the column, i.e., axial dispersion, fluid-to-particle mass transfer, intraparticle diffusion, and adsorption/desorption were calculated. Intraparticle diffusion was shown to have a dominant contribution to band broadening. The surface diffusion coefficient (D-s) showed a positive concentration dependence which could explain the dependence of the lumped mass transfer rate coefficient on the enantiomer concentration. It is likely that the positive concentration dependence of D-s could be explained by the heterogeneity of the surface of the stationary phase and that the distribution of adsorption energy on the surface of the imprinted polymer has an exponential decay profile.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

The analysis of experimental results in reversed-phase liquid chromatography (RPLC) allows further discussion of the restricted diffusion model of surface diffusion formulated on the basis of the absolute rate theory. Chromatographic data were acquired on different RPLC systems with two series of homologous compounds, several stationary phases having different alkyl ligand densities and ligands of various lengths, and methanol/ water mobile phases of different compositions, The enthalpy-entropy compensation observed and the linear free energy relationships found for surface diffusion suggest that the surface diffusion mechanism remains probably the same in all RPLC conditions studied, Whereas the isosteric heat of adsorption approaches zero with decreasing retention, the activation energy of surface diffusion tends toward a finite limit and the surface diffusion coefficient tends toward a value near the corresponding molecular diffusivity. These results support the validity of the restricted diffusion model. The influence of different factors on the validity of this model (i.e., the activation energy and the frequency factor of surface diffusion, and the surface tortuosity) was also considered.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

The accuracy of the method of elution by characteristic point (ECP) used to determine single component isotherms was studied numerically. Overloaded elution peaks were calculated using the equilibrium-dispersive model of nonlinear chromatography while varying the four parameters, i.e., the number of theoretical plates, the dimensionless Langmuir equilibrium constant, the retention and the loading factor, involved in the fundamental equations of the problem. Single component isotherms were estimated by analyzing the diffuse profile of the elution peaks by the ECP method. Similar results were obtained with the transport-dispersive model. The comparison of these calculated isotherms with the initial Langmuir isotherms provided detailed information on the influence of the mass transfer resistances on the accuracy of the isotherms afforded by the ECP method. The systematic error made on the isotherms depends on the experimental conditions, described by the four parameters. It is expected that this error could be eliminated by correcting the influence of nonequilibrium in the column on the basis of results of the nondimensional calculations. The concentration range of the objective isotherm which can be determined by the ECP method can also be predicted by numerical calculations. The usefulness of the correction strategy and the prediction of the concentration range were experimentally demonstrated. (C) 2000 Elsevier Science B.V. All rights reserved.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

A kinetic study was made on the mass transfer phenomena of bovine serum albumin (BSA) in two different anion-exchange columns (Resource-Q and TSK-GEL-DEAE-5PW). The analysis of the concentration dependence of the lumped mass transfer rate coefficient (k(m,L)) provided the information about the kinetics of the several mass transfer processes in the columns and the anion exchangers, i.e., the axial dispersion, the fluid-to-particle mass transfer, the intraparticle diffusion,and the adsorption/desorption. In the Resource-Q column, the intraparticle diffusion had a dominant contribution to the band broadening compared with those of the other processes. The surface diffusion coefficient (D-s) Of BSA showed a positive concentration dependence, by which the linear dependence of k(m,L) on the BSA concentration seemed to be interpreted On the other hand, in the TSK-GEL-DEAE-5PW column, the contribution of the adsorption/desorption was also important and almost same as that due to the intraparticle diffusion. There are some differences between the intrinsic properties of the mass transfer kinetics inside the two anion exchangers. It was likely that the positive concentration dependence of D-s was explained by the heterogeneous surface model. (C) 2000 Elsevier Science B.V. All rights reserved.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

The thermodynamic properties of surface diffusion in reversed-phase liquid chromatography (RPLC) were analyzed in connection with the thermodynamics of surface diffusion;in gas chromatography systems and of phase equilibrium in RPLC. The results suggest that the activation energy of surface diffusion in RPLC consists of only two contributions, corresponding to a hole-making and a bend-breaking process. The former is dose to the activation energy of the mobile phase viscosity; the latter is correlated with the isosteric heat of adsorption (Q(st)), by a numerical coefficient between 0.5 and 0.6. The validity of these results was proved by the analysis of correlations between the surface diffusion coefficient (D-s) and the adsorption equilibrium constant (linear free energy relation), between D-s and the boiling point of the sample components, and between the ratio of D-s to the molecular diffusivity and Q(st). These results support a restricted diffusion model, proposed earlier as an approximation of the mass transfer mechanism of surface diffusion. The restricted diffusion model provides consistent interpretations for the intrinsic thermodynamic properties of surface diffusion in RPLC.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Using numerical calculations of elution peak profiles, an explanation of the fronting behavior of elution peaks in linear chromatography was found in certain radial distributions of the mobile phase flow velocity and local bed efficiency. Fronting peaks are observed only if the flow velocity is higher in the wall region than in the center part of the column and the local efficiency is lower near the wall than in the center. By contrast, tailing or symmetrical peaks are observed if only the how velocity or the local efficiency are radially heterogeneous. The degree of peak fronting increases with increasing amplitude of the radial distributions. The influence of the radial heterogeneity of the flow velocity on the degree of peak fronting is more severe for high than for low efficiency columns. An equation is suggested to correlate peak fronting behavior for columns of different efficiencies and a procedure proposed for the estimation of the radial distributions of the flow velocity and the local efficiency by analyzing some characteristics of asymmetric peaks. (C) 1999 Elsevier Science B.V. All rights reserved.

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Language：English   Publishing type：Research paper (scientific journal)  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

A recent study of the mass transfer kinetics of (-)- or S-Troger's base (TB) between ethanol and microcrystalline cellulose triacetate (CTA) allows an analysis of the concentration dependence of the mass transfer rate coefficient (k(m)). S-TB elutes before R-TB. The retention time of the both compounds decreases with increasing temperature. In this study, experimental data measured between 30 and 50 degrees C were analyzed to provide information on the kinetics of several mass transfer processes which take place in the chromatographic column, i.e., axial and intraparticle dispersion, the fluid-to-particle mass transfer, and the kinetics of adsorption/desorption at the actual adsorption sites. Intraparticle diffusion has the dominant contribution to band broadening at high flow-rates. Both intraparticle diffusivity and the surface diffusion coefficient exhibit a small concentration dependence. The positive dependence of k(m) on the concentration of S-TB seems to result from the properties of the adsorption/desorption kinetics and can be interpreted by considering the phase equilibrium properties. A quantitative analysis of the activation energy of the mass transfer kinetics of S-TB in the CTA column was also attempted. (C) 1999 Elsevier Science B.V. All rights reserved.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Surface diffusion data obtained for a reversed-phase liquid chromatographic system (octadecylsilyl silica gel and a 70/30 (v/v) methanol/water solution) were analyzed in relation to their molecular diffusivity (D-m). The adsortate-adsorbent interactions between the studied compounds and the stationary phase were taken into account. The surface diffusion coefficient (D-s) depends on the mobile-phase composition, especially on the nature and concentration of the organic modifiers. Differences between the values of D-s measured under various conditions stem probably from differences in D-m. It also seems that D-s tends toward D-m with decreasing retention factor. The surface diffusion mechanism was assumed to be a restricted molecular diffusion in a potential held of adsorption. A restriction energy for this diffusion (E-r) was introduced to correlate D-s with D-m. The ratio of E-r to the isosteric heat of adsorption (-Q(st))was found to be nearly constant, irrespective of the retention factor, with an average value of 0.32 for our phase system. An estimation procedure for D-s using the enthalpy-entropy compensation effect for the adsorption equilibrium is proposed. From the adsorption equilibrium constant at 298 K only, D-s could be estimated at different temperatures with an error less than similar to 50%.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：KLUWER ACADEMIC PUBL  

Adsorption characteristics were studied in a reversed-phase liquid chromatography consisting of an octadecylsilyl (ODS)-silica gel and ethanol/water mixture (70/30, v/v), and were compared with corresponding results obtained by using methanol/water and acetonitrile/water mixtures (70/30, v/v) as mobile phase. Similar tendencies were observed for some adsorption characteristics in the three chromatographic systems. However, the magnitude of the characteristics was not entirely identical in the three systems. Surface diffusion was dominant for intraparticle diffusion in the ODS-silica gel particles irrespective of the type of the organic modifiers in mobile phases. A few correlations were confirmed with regard to surface diffusion, i.e., an enthalpy-entropy compensation and a linear free-energy relation. The analogous correlations on surface diffusion phenomena suggest the similarity in the mechanism of surface diffusion in the three chromatographic systems.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

An estimation procedure of the radial heterogeneity of the distributions of the mobile phase flow velocity and of the local column efficiency was derived from a comparison of experimental data and of the characteristics of these tailing peaks calculated numerically. The analysis of these characteristics indicated that the radial heterogeneity of the packing density of a column is a cause of peak tailing. This analysis showed also that it is possible to correlate the radial fluctuations of the flow velocity and the apparent efficiency of different columns. The comparison of experimental data and calculated results suggested also a correlation between the radial distributions of the Bow velocity and of the column efficiency. Previous experimental data concerning the radial heterogeneity of column packings validated the correlation. Information on the degree of heterogeneity of the radial distributions of the flow velocity and the column efficiency were obtained by analyzing the peak width and the asymmetry factor of elution peaks. It was also found that the exponentially modified Gaussian distribution cannot provide a comprehensive representation of all types of tailing profiles in chromatography. (C) 1999 Elsevier Science B.V. All rights reserved.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

The correlation between the radial heterogeneity of a column and the tailing of the elution profiles of chromatographic peaks was studied using a numerical method. A parabolic distribution of the linear flow velocity of the mobile phase and of the column efficiency in the radial direction were assumed. Moment analysis showed that peak tailing takes place under such experimental conditions and that it increases with increasing range of radial variations of the flow velocity and the column efficiency. It was also found that the higher the column efficiency, the larger the effect of a given degree of radial heterogeneity on the extent of peak tailing. Peak tailing behavior of columns having different efficiencies could be correlated with each other by an equation. Some characteristic features of tailing peaks were analyzed in connection with the column radial heterogeneity. (C) 1999 Elsevier Science B.V. All rights reserved.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：CANADIAN SOC CHEMICAL ENGINEERING  

An estimation procedure of surface diffusion coefficient, D-s, in liquid phase adsorption was proposed. The procedure is based on a restricted diffusion model, in which D-s is correlated with molecular diffusivity by considering a restriction energy due to an adsorptive interaction between adsorbates and adsorbents. In some adsorption systems, D-s of different adsorbates could be calculated with an error less than about 50% from only one datum of each adsorption equilibrium constant. Irrespective of temperature, the procedure can be applied for the estimation of D-s even in a wide range of D-s of about 4 orders of magnitude.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：CHEMICAL SOC JAPAN  

Surface-diffusion data in a gaseous adsorption system using an octadecylsilyl-silica gel as an adsorbent were analyzed according to a restricted Knudsen diffusion model. A linear correlation was confirmed between the ratio of the restriction energy for Knudsen diffusion to the isosteric heat of adsorption, Q(st), and 1/(-Q(st)). It was proved that a linear correlation could be observed under the conditions that a linear free-energy relation and an enthalpy-entropy compensation in adsorption equilibrium were established. An estimation procedure of the surface-diffusion coefficient (D-s) was proposed based on the results. It was demonstrated that D-s of various adsorbates at given temperatures could be estimated with an error of less than about 50% from only one datum of the adsorption equilibrium constant measured at a different temperature. Similarly, D-s in gas-phase adsorption could be estimated from the evaporative energy of the adsorbates without experimental data.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SOC CHEMICAL ENG JAPAN  

An estimation procedure for the surface diffusion coefficient (D-s) is proposed for a reversed-phase liquid chromatographic system using an octadecylsilyl-silica gel and methanol/water mixtures. The procedure is based on a restricted molecular diffusion model for surface diffusion, in which D-s is correlated with molecular diffusivity by introducing restriction energy (E-r) due to an adsorptive interaction between adsorbates and adsorbents. The ratio of E-r to isosteric heat of adsorption (Q(st)) is linearly correlated with 1/(-Q(st)). It is indicated that the linear correlation between gamma (=E-r/(-Q(st))) and 1/(-Q(st)) can be observed when a linear free-energy relation and an enthalpy-entropy compensation effect in adsorption equilibrium are established. Though both E-r and gamma are empirical parameters, D-s at given temperatures and mobile phase compositions can be consistently calculated with an error less than about 20% from only one datum of adsorption equilibrium constant.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC ANALYTICAL CHEM  

The retention behavior of p-alkylphenols was studied in reversed-phase liquid chromatography using octadecylsilyl-silica gel and ethanol/water mobile phases. The results were compared with those in methanol/water systems. Linear correlations were observed between the logarithmic retention factor (ln k) and the carbon number of side chains in the solutes, irrespective of the type and volumetric fraction (phi) of the organic modifiers in the mobile phases. The straight lines measured at different phi converged at almost one point. By analyzing the slope of the linear correlations, a functional contribution of a methylene group to k and a reduction of the hydrophobic surface area of the solutes and octadecylsilyl ligands due to the retention were estimated. It was also attempted to analyze the characteristics of the retention in reversed-phase liquid chromatography on the basis of solvophobic theory.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC ANALYTICAL CHEM  

The mass-transfer characteristics were studied in a reversed-phase liquid chromatography consisting of an octadecylsilyl-silica gel and acetonitrile/water mixture (70/30, vol), and were compared with those obtained by using methanol/water (70/30, vol). In the two chromatographic systems, similar tendencies were observed for various adsorption characteristics. However, their absolute values were not entirely identical. Irrespective of the type of organic modifiers, surface diffusion was dominant for intraparticle diffusion. Similar correlations were also demonstrated with regard to the surface diffusion, i.e., the enthalpy-entropy compensation and the linear free-energy relation, suggesing a similarity in the surface migration mechanism in the two chromatographic systems. A few estimation procedures of the surface diffusion coefficient were proposed.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Surface diffusion phenomena of alkylbenzenes in reversed-phase liquid chromatography (RP-LC) using an octadecylsilyl-silica gel and methanol/water (70/30, v/v) were analyzed on the basis of a restricted molecular diffusion model, in which surface diffusion coefficient, D-s, was correlated with molecular diffusivity, D-m, by introducing a restriction energy, E-r. The average ratio of E-r to isosteric heat of adsorption Q(st), gamma, in RP-LC was about 0.3. It was also indicated that gamma at different temperatures could be represented as a linear function of the reciprocal of -Q(st) when a linear free-energy relation held and an enthalpy-entropy compensation for adsorption equilibrium was established. An estimation procedure of D-s was proposed on the basis of the results. It was demonstrated that D-s at a given temperature could be calculated with an error of less than about 10% from only one datum of the adsorption equilibrium constant.

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Language：Japanese   Publishing type：Research paper (bulletin of university, research institution)   Publisher：Toyama University  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SOC CHEMICAL ENG JAPAN  

Adsorption characteristics of organic compounds on an octadecylsilyl (ODS)-silica gel for two mobile phases, i.e., methanol/water (70/30, v/v) and acetonitrile/water (70/30, v/v) are compared. It is confirmed that the values of adsorption equilibrium constant, isosteric heat of adsorption, and activation energy of surface diffusion are smaller in 70 vol% acetonitrile than in 70 vol% methanol. On the contrary, the values of surface diffusion coefficient, D-s, are larger in 70 vol% acetonitrile than in 70 vol% methanol. These results indicated that the interaction between ODS ligands and solute molecules was weaker in 70 vol% acetonitrile than in 70 vol% methanol. The ratio of D-s to molecular diffusivity, D-m, is about 0.3 irrespective of chromatographic conditions, i.e., the type of organic modifiers and sample compounds, and temperature. It is possible to calculate D-s from D-m, which can be estimated by various correlations previously proposed in the literature. The almost constant ratio of D-s to D-m suggests the presence of a kind of correlation between surface and molecular diffusions.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST CHEMICAL ENGINEERS  

Based on the absolute-rate theory a consistent interpretation was provided for the dependence of surface-diffusion coefficient, D-s, on temperature and the amount adsorbed in various liquid-phase adsorption systems, such as the Langmuir-, Freundlich- and Jossens-type adsorption. It was demonstrated that a restricted molecular diffusion model for surface diffusion was useful for the analysis of the characteristic features of D-s. A formulation of D-s was derived based on the model and was applied to the analysis of surface-diffusion phenomena in various adsorption systems. The temperature dependence could be interpreted by assuming surface diffusion as an activated process. By taking into account the change in both the logarithmic slope of an adsorption isotherm and an adsorption potential, the concentration dependence of D-s could be interpreted irrespective of the type of the adsorption isotherms.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC ANALYTICAL CHEM  

A nondimensional plate height equation was proposed for the kinetic analysis of peak spreading in liquid chromatography. The equation was derived on the basis of the theory of moment analysis. The equation represents the correlation between two dimensionless parameters, the reduced plate height, h, and reduced velocity, v, with several other parameters including a surface diffusion coefficient. Characteristic features of the equation proposed were compared with those of several ordinary equations. The influence of each of the several parameters in the equation on the correlation between h and v was individually evaluated by numerical calculations. The influence of surface diffusion on h was significant at sufficiently large values of v. The contributions of a few mass-transfer processes in a column, i.e., axial dispersion, fluid-to-particle mass-transfer, and intraparticle diffusion, to h were separately evaluated. It was demonstrated that peak spreading phenomena in liquid chromatography could be numerically analyzed under various conditions according to the nondimensional equation.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Characteristics of surface diffusion phenomena were studied under low-loading or analytical conditions of reversed-phase Liquid chromatography. As mobile phases, methanol/water and acetonitrile/water mixtures were used. In both systems, several similar relationships were confirmed for the enthalpy-entropy compensation effect, the linear free-energy relation, and some correlations between the surface diffusion coefficient, D-s, and mobile-phase composition, phi, and between the ratio of D-s to molecular diffusivity and phi. Similarity of the correlations indicated that the surface diffusion mechanism was essentially identical irrespective of the type of the organic modifiers. A strong influence of phi on D-s was confirmed. A nomograph concerning corresponding mobile-phase compositions for D-s as well as for adsorption equilibrium constant was proposed for the both mobile-phase systems. On the basis of the several correlations, D-s under various conditions in low-concentration systems can be estimated.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

A model for surface diffusion was proposed on the basis of molecular diffusion. Surface diffusion was regarded as a molecular diffusion restricted due to the adsorptive interaction between adsorbate molecules and the surface of adsorbents. The restricted molecular diffusion model was formulated by applying the absolute rate theory. Experimental data of surface diffusion coefficient in reversed-phase liquid chromatography were analyzed by considering the influence of the adsorptive interaction. Though accurate specification of a frequency factor was not sufficient, characteristic features of the activation energy of surface diffusion could be quantitatively interpreted. The activation energy of surface diffusion was divided into two contributions of a hole-making step and a jumping one. The former was correlated with the evaporative energy of a solvent, not of an adsorbate, and the latter with the isosteric heat of adsorption of the adsorbate. The validity of the concept was proved by applying the model to the quantitative analysis of surface diffusion data on other various liquid phase adsorption previously published. An interpretation was provided for various correlations between the activation energy of surface diffusion and isosteric heat of adsorption in the liquid phase adsorption systems.

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Language：English   Publishing type：Research paper (scientific journal)  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

The influence of volumetric composition of acetonitrile in a mobile phase on adsorption characteristics of reversed-phase liquid chromatography using octadecylsilyl (ODS)-modified silica gel was studied by the pulse response method and the moment analysis. The results were compared with those obtained for the reversed-phase system consisting of ODS-silica gel and methanol/water mixtures, In both systems, surface diffusion was dominant for intraparticle diffusion in ODS-silica gel particles, The contributions of three mass transfer steps in a column to peak broadening were of about the same order of magnitude. The activation energy of surface diffusion, E-s, was found to be larger than the isosteric heat of adsorption, Q(st). Because similar tendencies were observed for these adsorption characteristics, adsorption mechanisms may be analogous in both chromatographic systems. However, absolute values of the adsorption equilibrium constant, K, the decreasing ratio of hydrophobic surface area, Delta A/A, Q(st), and E-s for acetonitrile/water systems were smaller than the corresponding values for methanol/water systems, Oppositely, greater values of D-s were obtained for acetonitrile/water systems, It was concluded that the interaction between ODS ligands and adsorbate molecules was weaker compared with that in methanol/water mobile-phase systems when acetonitrile was used as an organic modifier in a mobile phase of reversed-phase liquid chromatography.

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society for Analytical Chemistry  

The adsorption characteristics of reversed-phase liquid chromatography were studied by the chromatographic method and a moment analysis. Octadecylsilyl-silica gel was used as a stationary phase and an acetonitrile-water (70/30,v/v) mixture as a mobile phase. The equilibrium, kinetic, and thermodynamic properties of adsorption phenomena in the system were elucidated, and compared with those in a reversed-phase system using a methanol-water (70/30,v/v) mixed solvent as a mobile phase. The magnitude of the interaction between the adsorbate molecules and octadecyl ligands in 70 vol% acetonitrile was weaker than that in 70 vol% methanol. In both adsorption systems, the surface diffusion was dominant for intraparticle diffusion. Surface diffusion phenomena were considered from the viewpoint of the thermodynamic properties. The establishment of an enthalpy-entropy compensation effect was confirmed for surface diffusion phenomena. The differences in the mass-transfer properties in both reversed-phase liquid chromatographic systems were quantitatively elucidated from equilibrium, kinetic, and thermodynamic points of view

DOI： 10.2116/bunsekikagaku.46.579

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Other Link： http://dl.ndl.go.jp/info:ndljp/pid/10894093

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST CHEMICAL ENGINEERS  

The effect of solvent and mobile-phase composition on adsorption characteristics in liquid-phase absorption is studied. Comparing experimental adsorption data for several organics in both gas- and liquid-phase systems confirms that adsorption equilibrium constant K and isosteric heat of adsorption Q(st) are smaller than those in corresponding gaseous systems. The logarithm of K almost linearly increases as methanol composition decreases. Solvophobic theory applied quantitatively analyzes these solvent effects. Estimation methods for three parameters influence calculation results: solvent effects on K can be quantitatively analyzed; the adsorbability of adsorbates can be estimated from the value of Delta G(solv) for each homologue in a reversed-phase liquid chromatographic system; and the solvent effect on Q(st) cannot be satisfactorily interpreted. It is, however, confirmed that Q(st) is influenced by a solvent and an apparent small value is observed in liquid-phase adsorption.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST CHEMICAL ENGINEERS  

Adsorption characteristics of reversed-phase liquid chromatography and influence of solvent composition on the characteristics are studied by the chromatographic method and the moment analysis. Adsorption equilibrium constant increases by adding hydrophobic increments into adsorbate molecules. Contributions of fluid-to-particle mass transfer and intraparticle diffusion to mass-transfer resistance in the octadecylsilyl-silica gel (ODS) column are almost equally great. Surface diffusion is dominant for the intraparticle diffusion in ODS. The logarithm of the surface diffusion coefficient linearly increases with an increase in methanol fraction in the range from 40 to 100 vol. %. In liquid-phase adsorption, activation energy of surface diffusion is greater than the isosteric heat of adsorption and both increase when methanol fraction decreases in the range from 40 to 100 vol. %. An empirical correlation based on experimental data proposed estimates surface diffusion coefficients from physical properties of adsorbates.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SOC CHEMICAL ENG JAPAN  

The effect of chain length of alkyl bonded phases on adsorption characteristics, especially mass transfer phenomena and thermodynamic parameters, in reversed-phase liquid chromatography was studied by the chromatographic method and moment analysis. Adsorption equilibrium constant, isosteric heat of adsorption and activation energy of surface diffusion increased with an increase in length of alkyl ligands in short chain regions. On the contrary, surface diffusion coefficient increased with a decrease in alkyl chain length. Change of all the parameters decreased when the carbon number of the alkyl ligands was about 8 and above. Almost the same adsorption characteristics were observed when C-8 and C-18 packing materials were used as an adsorbent. It is concluded that only parts of long alkyl chains contribute to adsorption phenomena in reversed-phase liquid chromatography. The contribution of surface diffusion to intraparticle diffusion was significant and increased with an increase in alkyl chain length.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Characteristics of mass-transfer phenomena on the surface of adsorbents in reversed-phase chromatography were studied by the chromatographic method and moment analysis. Enthalpy-entropy compensation occurs for surface diffusion in various systems of reversed-phase chromatography. The mechanism of surface diffusion seems to be essentially identical regardless of adsorption conditions. The linear free-energy relation holds in reversed-phase liquid chromatographic systems. Analyzing the slope of the linear relations, it is concluded that the activation energy of surface diffusion is essentially smaller than the isosteric heat of adsorption in liquid-phase adsorption as well as in gaseous systems though the heat of adsorption is experimentally determined to be smaller than the activation energy. Surface diffusion coefficients were correlated to physical properties of adsorbates. Concentration dependence of surface diffusion coefficient was explained by the chemical potential driving force model. An estimation method of the surface diffusion coefficient at each given temperature and amount adsorbed in reversed-phase liquid chromatography was proposed.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SOC CHEMICAL ENG JAPAN  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST CHEMICAL ENGINEERS  

Adsorption rates and thermodynamic parameters were determined for the gas-phase adsorption of n-alkanes and benzene derivatives on octadecylsilyl-silica gel (ODS) by chromatographic measurement and moment analysis. Thermodynamic characteristics of adsorption phenomena on ODS were similar to those on the surface. The contribution of intraparticle diffusion to mass-transport resistance was dominant in the ODS column, and the role of surface diffusion was significant for the intraparticle diffusion. The values of the surface diffusion coefficient were of the order of 10(-5) cm2/s and could be estimated by assuming that the surface migration on ODS is a tracer diffusion of an adsorbate molecule in n-octadecane.

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Language：Japanese   Publishing type：Thesis (other)  

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Language：English   Publishing type：Research paper (scientific journal)  

Intraparticle diffusion of p-tert-octylphenol in octadecylsilyl-silica gel (ODS) were studied by the chromatographic technique and the method of moment at zero and various surface coverages. Surface diffusion is dominant for the intraparticle diffusion in ODS. Surface diffusion coefficient increased with an increase in the amount adsorbed. The positive concentration dependence of the surface diffusion coefficient was interpreted in terms of diffusion by chemical potential driving force. Analyses of adsorption equilibrium and thermodynamic parameters suggested energetical uniformity of the surface of ODS. The influence of a solvent on characteristics of liquid phase adsorption is also discussed. © 1993, Kodansha Ltd.

DOI： 10.1016/S0167-2991(08)63545-4

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST CHEMICAL ENGINEERS  

Intraparticle diffusion and adsorption equilibrium on octadecylsilyl-silica gel (ODS) were studied. As an adsorbate, p-tert-octylphenol (PTOP) was employed. The intraparticle diffusion coefficient was measured by the chromatographic technique and the moment analysis at zero and several surface coverages. Adsorption isotherms can be correlated by the Langmuir equation. The isosteric heat of adsorption and the activation energy of surface diffusion were constant regardless of the amount adsorbed. These results suggest that ODS has an energetically homogeneous surface. The effect of solvent on isosteric heat of adsorption in the liquid system was discussed qualitatively by the solvophobic theory. Surface diffusion coefficient of PTOP on ODS was of the order of 10(-7) to 10(-6) cm2/S. Surface diffusion was dominant for the intraparticle diffusion in ODS, and its coefficient increased with an increase in the amount adsorbed. Positive concentration dependence of the surface diffusion coefficient was interpreted in terms of diffusion by potential chemical driving force.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SOC CHEMICAL ENG JAPAN  

A simple method for the estimation of an adsorption isotherm based on the analysis of an experimental desorption curve was studied. As an adsorption isotherm, the Toth equation was employed. Two simple methods taking into account the effect of a mass transfer rate were proposed. In the two methods, however, concentration dependence of an overall mass transfer coefficient on the amount adsorbed was neglected. The two methods and the equilibrium desorption method were applied to several liquid phase adsorption systems to determine adsorption isotherms. It was concluded that the two methods proposed here gave adsorption isotherms within about 2% error in most cases, and that the accuracy of the equilibrium desorption method was insufficient in a case where the value of the dimensionless longitudinal distance or bed length (Z) is small. The conditions under that the equilibrium desorption method can be used were clarified by analyzing theoretical desorption curves numerically calculated. The error of the equilibrium desorption method is governed by the combination of the dimensionless equilibrium and kinetic parameters r, Z and Toth equation parameter t. The error decreases as non-linearity of an adsorption isotherm is emphasized, and as the value of Z increases. By using the three mothods properly according to the experimental conditions, an adsorption isotherm can be estimated within about 2% error. Only two preliminary data, namely one desorption curve and one pulse response curve, are required.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Society of Chemical Engineers, Japan  

An industrial-scale reversed-phase liquid chromatograph was developed by using a multicolumn system. Its use reduced the volume of solvent and the operation time for chromatography, to about one -tenth of those required in a conventional elution. As a result, the maximum concentration of the objective component increased approximately fifteen times.<BR>A simulation method was used to optimize the operational conditions of the column system. The validity of the calculated result was confirmed experimentally.<BR>In industrial-scale liquid chromatography the multicolumn system effectively increases the efficiency of the whole purification process.

DOI： 10.1252/kakoronbunshu.15.475

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Other Link： https://jlc.jst.go.jp/DN/JALC/00225156995?from=CiNii

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society for Analytical Chemistry  

It is found that the extraction constant K_<ex>, for the ion-pair extraction systems is made up of three independent constants (individual extraction constants), K_e, K_a, and K_s in accordance with the equation: log K_<ex>= log K_c + log K_a + log K_s……………(1) where the subscripts c, a, and s denote cation, anion, and solvent, respectively. The anion, cations, and solvents studied were 7-iodo-8-quinolinol-5-sulfonic acid (ferron), eight cationic surfactants and 1,2-dichloroethane, dichloromethane, and chloroform. Cationic surfactants used in this work are alkyltrimethylammonium salts with alkyl chain lengths from 10 to 18 methylene groups, and several quaternary ammonium salts. Logarithm K values for several cations, anion, and solvents were calculated from experimental values of log K_<ex> by tentatively assigning the log K values 1.0 and 1.0 to ferron and chloroform, respectively, as reference value. It was also shown that the association constant, K_A and the distribution constant, KD are made up of independent constants K_<A,c>, K_<A,a>, (individual association constants) and K_<D,c>, K_<D,a>, K_s (individual distribution constants) , respectively, in accordance with the equations: log K_A = log K_<A,c> + log K_<A,a>…………………(2) log K_D=log K_<D,c>+log K_<D,a>+log K_s………(3) where subscript c, a, and s have the same meaning as in equation (1). Experimental data, are presented to show the validity of the above three equations.

DOI： 10.2116/bunsekikagaku.32.11_678

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Other Link： http://dl.ndl.go.jp/info:ndljp/pid/10890346

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

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Language：Japanese   Publishing type：Article, review, commentary, editorial, etc. (other)   Publisher：日本分析化学会  

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Language：English   Publishing type：Book review, literature introduction, etc.   Publisher：WILEY-V C H VERLAG GMBH  

Monolithic stationary phases and columns have rapidly become highly popular separation media for liquid chromatography, in spite of their recent discovery. However, their most important features have not yet been completely clarified. A complete understanding of their performance and of their intrinsic characteristics will require the systematic acquisition of many series of reliable experimental data and their consistent analysis from different points of view. Progress in their design and production requires now that the chromatographic behavior of monolithic columns be studied in close connection with their physico-chemical and structural properties. The main goal of this review is to summarize fundamental information on some physico-chemical and chromatographic characteristics of monolithic stationary phases and columns for RPLC. The material reviewed deals only with silica-based monolithic columns. First, structural information on the porosities and the size of the pores in monolithic columns is reported. Second, results of chromatographic studies that deal with the characterization of monolithic columns are summarized. Third, results of detailed studies made on the adsorption equilibrium and the surface heterogeneity of monolithic stationary phases are presented. Finally, results on the mass transfer kinetics in monolithic columns derived from the applications of the classical random-walk model and of the moment theory to a new model of the monolith are discussed.

DOI： 10.1002/jssc.200401772

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Language：English   Publishing type：Book review, literature introduction, etc.   Publisher：WILEY-V C H VERLAG GMBH  

Fundamental studies of the mass transfer kinetics are as essential as those of the retention equilibrium for a detailed understanding of the characteristics and the mechanisms of chromatographic separations. The acquisition of a large amount of reliable experimental data and of meaningful results is necessary for any further progress of our knowledge of kinetics. The main goal of this review is to provide information on the methods used to perform accurate measurements and on the data analysis procedures used for deriving the kinetic parameters characterizing mass transfer in HPLC. First, the general characteristics of several methods of determination of some kinetic parameters are briefly reviewed. Secondly, we give detailed explanations of the experimental conditions of the pulse on a plateau method (i.e., elution chromatography on a plateau of finite concentration or pulse response method) and of the data analysis procedures based on moment analysis. Thirdly, we explain some important requirements for the acquisition of appropriate experimental data and discuss corrections to be applied when deriving several kinetic parameters. Fourthly, we discuss the accuracy of the kinetic parameters derived from the pulse on a plateau method and from moment analysis. Finally, some results concerning the mass transfer kinetics in RPLC systems are demonstrated as examples.

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Language：English   Publishing type：Book review, literature introduction, etc.   Publisher：MARCEL DEKKER  

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Language：Japanese   Publishing type：Article, review, commentary, editorial, etc. (scientific journal)   Publisher：The Japan Society for Analytical Chemistry  

An analytical study was made concerning mass-transfer phenomena in reversed-phase liquid chromatography (RP-LC). A moment method was applied for analyzing the properties of chromatographic peaks measured under various conditions related to sample substances as well as stationary and mobile phases. First moment analyses provided some pieces of information concerning the mass-transfer equilibrium in RP-LC. The isosteric heat of adsorption (-Q_<st>) was smaller than the corresponding heat of vaporization. The relatively small value of -Q_<st> could be explained by solvophobic theory. From second moment analyses, it was indicated that the contribution of intraparticle diffusion to the overall mass-transfer resistance in a column was usually important, and that surface diffusion played a significantly dominant role for mass transfer in RP packing materials. The activation energy of the surface diffusion (E_s) was larger than -Q_<st> in RP-LC. The correlation between E_s and Q_<st> could be quantitatively interpreted based on the absolute rate theory by assuming that surface diffusion was an activated process similar to molecular diffusion in the liquid phase. The establishment of both an enthalpy-entropy compensation effect and a linear free-energy relation was confirmed irrespective of the separation conditions in RP-LC. A nondimensional rate equation was derived on the basis of moment analysis theory. The equation consists of several terms representing the contributions of mass-transfer processes, such as molecular diffusion, eddy diffusion, fluid-to-particle mass transfer, and intraparticle pore and surface diffusions, to peak spreading. The influence of some operational parameters on the column efficiency was numerically analyzed while considering the individual contribution of each term. It was demonstrated that fundamental studies of surface diffusion provided some essential pieces of information for elucidating the separation mechanism in RP-LC.

DOI： 10.2116/bunsekikagaku.47.769

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Other Link： http://dl.ndl.go.jp/info:ndljp/pid/10894370

Language：Japanese   Publishing type：Article, review, commentary, editorial, etc. (other)   Publisher：日本吸着学会  

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Language：Japanese   Publishing type：Article, review, commentary, editorial, etc. (other)   Publisher：日本吸着学会  

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Language：Japanese   Publishing type：Article, review, commentary, editorial, etc. (bulletin of university, research institution)  

CiNii Article

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Other Link： http://hdl.handle.net/2261/49272

Language：Japanese   Publishing type：Article, review, commentary, editorial, etc. (bulletin of university, research institution)  

CiNii Article

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Other Link： http://hdl.handle.net/2261/49258

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