Solvophobic theory chromatography

Separations in hydrophobic interaction chromatography have been modeled as a function of the ionic strength of the buffer and of the hydrophobicity of the column, and tested using the elution of lysozyme and ovalbumin from octyl-, butyl- and phenyl-Sepharose phases.2 The theoretical framework used preferential interaction analysis, a theory competitive to solvophobic theory. Solvophobic theory views protein-surface interaction as a two-step process. In this model, the protein appears in a cavity in the water formed above the adsorption site and then adsorbs to the phase, with the free energy change... 

Solvents, UV cut-olf values, 70 Solvents, miscibility, 75 Solvophobic effect, 201,203 Solvophobic inleHlclidHk, IS2, 20i Solvophobic ion chromatography, 242 Solvophobic theory, 141,148,152,155, 158, 202, 203, 226, 228, 246 8omatostedn, 263,290 Sorbents, polymeric, 127 Sorption isottom, 159 Soiption kineties, efbet on column effi-cieney in RPC, 227 Speed of aepantion, optimization [Pg.172]

The retention mechanism is not yet fully understood. The solvophobic theory does not account for any interaction in the stationary phase, which plays a passive role. The partition mechanism as described by Dill and Dorsey (27) is generally accepted. The most relevant feature is the linear plot of In k versus carbon number in a homologous series (Fig. 10), which is similar to what is observed in isothermal gas-liquid chromatography. Retention is governed mainly by hydro-... 

Meliander, W. R., Corradini, D., and Horvath, C. (1984). Salt-medated retention of proteins in hydrophobic-interaction chromatography. Application of solvophobic theory. J. Chromatogr. 317, 67-85. 

In spite of widespread applications, the exact mechanism of retention in reversed-phase chromatography is still controversial. Various theoretical models of retention for RPC were suggested, such as the model using the Hildebrand solubility parameter theory [32,51-53], or the model supported by the concept of molecular connectivity [54], models based on the solvophobic theory [55,56) or on the molecular statistical theory [57j. Unfortunately, sophisticated models introduce a number of physicochemical constants, which are often not known or are difficult and time-consuming to determine, so that such models are not very suitable for rapid prediction of retention data. 

The cavity model of solvation provides the basis for a number of additional models used to explain retention in reversed-phase chromatography. The main approaches are represented by solvophobic theory [282-286] and lattice theories based on statistical thermodynamics [287-291]. To a lesser extent classical thermodynamics combining partition and displacement models [292] and the phenomenological model of solvent effects [293] have also been used. Compared with the solvation parameter model all these models are mathematically complex, and often require the input of system variables that are either unknown or difficult to calculate, particularly for polar compounds. For this reason, and because of a failure to provide a simple conceptual picture of the retention process in familiar chromatographic terms, these models have largely remained the province of the physical chemist. 

Figure 4,14. Diagram of the thermodynamic cycle used to explain retention in reversed-phase chromatography by solvophobic theory. Na = Avogadro number, AA = reduction of hydrophobic surface area due to the adsorption of the analyte onto the bonded ligand, y = surface tension, = energy correction parameter for the curvature of the cavity, V = molar volume, R = gas constant, T = temperature (K), Pq = atmospheric pressure, AGydw.s.i a complex function of the ionization potential and the Clausius-Moscotti functions of the solute and mobile phase. Subscripts i = ith component (solute or solvent), S = solute, L = bonded phase ligand, SL = solute-ligand complex, R = transfer of analyte from the mobile to the stationary phase (retention), CAV = cavity formation, VDW = van der Waals interactions, ES = electrostatic interactions.

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