Unified theory of retention and selectivity in liquid chromatography. 2. Reversed-phase liquid chromatography with chemically bonded phases

Abstract

1045hence increases the rigidity of the polymer.(ii) In the second explanation, the assumption is made that the compressibility of PVA in the adsorbed state is the same as in solution; i.e., no structural changes occur on adsorption. However, in this model the adsorbed PVA hinders the surface chemical reaction between the surface sites (sulfate and sulfonate end groups) and counterions (H+) due to dipole-ion interactions between alcohol segments of the PVA and the end groups of the latex. Ottewill and Vincent26 made a study of adsorption and wetting behavior of 1-alkanols of polystyrene latex particles. From the adsorption isotherm of 1-butanol on the latex particles, they reached the conclusion that the interaction occurred between hydroxyl groups on the butanol molecule and the hydrophilic sites of the surface. They also concluded that adsorption of alcohol molecules on the charged hydrophilic sites leads to desorption of the counterions from the inner part of the double layer.In Figure 6, the solid line represents the compressibility of the latex (from Figure 3) while the points are the compressibility calculated from data with the PVA-coated latex assuming that the compressibility observed is of the right order of magnitude to be explained by the elimination of the relaxation compressibility arising from the surface chemical reaction.With the present experimental evidence, it is not possible to distinguish between the two possible explanations given above.Acknowledgment. We are indebted to Dr. C. A. Young, who carried out the adsorption isotherms of various PVA samples on polystyrene latex samples, to Mr. M. J. Castle and Dr. M. C. Wilkinson of the Chemical Defense Establishment, Porton Down, Salisbury, Wiltshire, England, for determination of the glass transition temperature of the latex A and sucrose density centrifuge density measurements on various latices. Latex A was prepared by one of the authors (M.E.G.) in Bristol University, U.K. A sample of this latex was used in the present work with the kind permission of Prof. D. H. Everett. This research has been supported by the Office of Naval Research.Polystyrene, 9003-53-6; sodium styrenesulfonate-styrene copolymer, 39307-76-1; poly(viny1 acetate), Registry No. 9003-20-7.A lattice model is developed and used to study retention and selectivity in reversed-phase liquid chromatography (RPLC). The composition and the structure of the stationary phase are analyzed as a function of the chain length of the chemically bonded phase (CBP), the intrinsic chain stiffness, the surface coverage, and the nature of the mobile-phase solvent, for neat solvents and binary mixtures. The solute distribution process (retention mechanism) is investigated. Distribution constants are analyzed as a function of the above variables, the nature of the solute, and the temperature. The general behavior of the model system and the behavior of the special limiting cases of completely collapsed and fully extended CBP chains are considered, the former limiting case being particularly signifi...

Chromatographic activity of residual silanols of alkylsilane derivatized silica surfaces

“…In this respect, the solvophobic retention theory [27][28][29] has earned significant acceptance. Based on this solvophobic theory, Galushko has proposed a calculatory model [30] for the retention of solutes in reversed-phase HPLC that appears able to predict retention factors for various solutes on different stationary phases for RP-HPLC with fairly good accuracy [31].…”

Partitioning of alkylbenzenes and aliphatic-alcohols between hexadecane and methanol-water mixtures

“…Hexadecane, component h, is composed of group type I, the methyl and methylene groups. Expanding eqs (3), (4), and (5) to include the group types and substituting the results into eq (7), the hexadecane/methanol-water partition coefficient is now given by (8) where ri. is the number of segments of group type i in the solute molecule (r. = rl.…”

“…RPLC involves the distribution of a nonpolar or moderately polar solute between a polar mobile phase (the eluent) and a relatively nonpolar stationary phase [3]. The stationary phase is made up of silica gel particles to which n -alkyl chains (often, n -octadecyl) have been bound.…”

Reverse-High Performance Liquid Chromatography Mechanism Explained by Polarization of Stationary Phase

“…Currently, papers consider simultaneous contributions from more than one retention mechanism: adsorption on free silanols and partitioning into the chemically bonded phase [15], with preponderance of a mechanism that is largely partitioning, particularly for C 18 stationary phases and for small non-polar solutes [3,16,17,18,19]. Examples of this kind of theories are the unified molecular theory model of Martire and Boehm [16] or the statistical-mechanical theory [10].…”

“…Examples of this kind of theories are the unified molecular theory model of Martire and Boehm [16] or the statistical-mechanical theory [10]. Both of these theories consider that retention energies are dominated by partitioning of eluates into the bonded-phase, although monomolecular layer cannot be considered a phase in classical thermodynamics, and although they cannot explain why retention of analytes on the stationary phase changes when solid phase particles become saturated by organic modifier [20].…”