Adsorption Characteristics of Reversed-phase Liquid Chromatography with Various Alkyl Bonded Phases.

1997

J. Phys. Chem. B

Self Cite

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.

Section: Resultssupporting

confidence: 86%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Analysis of Surface Diffusion Phenomena in Liquid Phase Adsorption

1997

J. Phys. Chem. B

Self Cite

“…Similar experimental results have been reported for surface diffusion phenomena in liquid phase adsorption. 5,7,8,[20][21][22][23] Under such conditions, it is energetically advantageous for adsorbed molecules to be desorbed from a surface to a bulk phase than to migrate on the surface, suggesting that surface diffusion phenomena are absent. In previous papers 5,20 the authors attempted to quantitatively explain the situation by applying solvophobic theory, that the results were partially attributed to the influence of a solvent on the liquid phase adsorption.…”

Section: Second Moment Analysismentioning

confidence: 99%

“…The authors have studied mass-transfer phenomena in RP-LC using mainly methanol/water and octadecylsilyl (ODS)-silica gel as mobile and stationary phases. [5][6][7][8] Pulse-response experiments were made under various conditions of the solutes as well as the stationary and mobile phases. Their type, composition, and concentration were changed.…”

mentioning

confidence: 99%

Effect of the Type of Organic Modifiers on Mass Transfer in Reversed-Phase Liquid Chromatography

1998

ANAL. SCI.

Self Cite

Methanol/water and acetonitrile/water mixtures have generally been used as a mobile phase in reversedphase liquid chromatography (RP-LC). Chromatographic separations are significantly affected by the mobile-phase conditions, such as the type and composition of the organic modifiers. A number of studies have been made on the influence of the mobile-phase conditions on the retention behavior in RP-LC in connection with the specification of the separation mechanism and with the establishment of optimization strategies for chromatographic conditions.It is also essential to analyze the chromatographic processes from the viewpoints of mass-transfer kinetics and the thermodynamic properties as well as the retention behavior in order to understand the separation mechanism in RP-LC. However, there have not been very many kinetic studies on mass-transfer phenomena in RP packing materials [1][2][3][4] , in contrast to the extremely extensive studies on chromatographic retention. The authors have studied mass-transfer phenomena in RP-LC using mainly methanol/water and octadecylsilyl (ODS)-silica gel as mobile and stationary phases. 5-8Pulse-response experiments were made under various conditions of the solutes as well as the stationary and mobile phases. Their type, composition, and concentration were changed. Some items of information about the retention behavior, mass-transfer rates, and thermodynamic properties in RP-LC were obtained.This paper is concerned with the influence of the type of organic modifiers in the mobile phases on the chromatographic properties in RP-LC. The information about the retention behavior, mass-transfer rates, and thermodynamic properties were determined by using a mixture of acetonitrile and water (70/30, v/v) and an ODS-silica gel as a mobile and stationary phase. In a previous paper 9 , the authors reported on results of a similar study using alkylbenzenes and p-alkylphenols as solutes. In this study, the characteristics of the RP-LC system were analyzed in more detail using more solutes than before. In particular, it was attempted to correlate the surface diffusion coefficient (D s ) with various physical parameters of the solutes. The results in 70 vol% acetonitrile were compared with those in 70 vol% methanol. On the basis of the results, a few estimation procedures of D s have been proposed. In this paper, the mass-transfer and concentration phenomena of solutes from a bulk mobile phase to the surface of ODS-silica gel is represented by the word "adsorption" in a wide sense. The mechanism of the mass transfer, i.e., "partition or adsorption", is not defined. Experimental Column and reagentsSeveral properties of an ODS column (YMC) and the experimental conditions are given in Table 1. An ODS column packed with relatively large ODS-silica gel particles was used in order to make it easy to quantitatively analyze the influence of the mass-transfer rates on the peak spreading. The volumetric composition of acetonitrile was 70%, which was selected as a typical value of mobile-phase compositio...

Model for surface diffusion in liquid‐phase adsorption

1997

AIChE Journal

Based on the absolute-rate theoly, a consistent interpretation was provided for the dependence of surface-difiion coeffiient, D,, on temperature and the amount adsorbed in various liquid-phase adsorption systems, such as the Langmuir-, Freundlichand 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 0,. A formulation of D, 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 d i f i i o n 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 0, could be interpreted irrespective of the type of the adsorption isotherms.