Solvophobic Theory and Normalized Free Energies of Nonpolar Substances in Reversed Phase Chromatography

Abstract

A simplified version of the solvophobic theory is employed to reexamine a large set of retention data with nonpolar and weakly polar eluites in reversed phase chromatography (RPC) to test certain predictions by the theory and to clarify further the roles of the mobile and the stationary phase in the retention process. The free energy of retention in RPC is expressed in terms of the nonpolar surface area of the eluite, the pertinent interfacial tensions, and the energetics of eluite−stationary phase interactions in the gas phase. Within this framework changes in retention free energy per unit water accessible nonpolar surface area are evaluated in the entire range of the organic modifier concentration by using thermodynamic data for the retention of nonpolar eluites on alkyl silica bonded phase in gas chromatography and for the transfer of nonpolar solutes from the hydroorganic solvent to the gas phase. The normalized retention free energy parameters thus obtained according to the theory are in excellent agreement with those evaluated from experimental retention data using methanol, acetonitrile, tetrahydrofuran, and 2-propanol as organic modifiers in RPC. Furthermore, these parameters are found to be the same from column to column for a particular stationary phase and therefore characterize the RPC retention process. Analysis of experimental retention data obtained with various bonded phases indicates that the stationary phase chain length has a much smaller effect on the changes in selectivity of nonpolar aliphatic eluites than the mobile phase concentration. The results demonstrate the usefulness of the solvophobic theory for the evaluation of physicochemical parameters associated with retention of hydrocarbonaceous eluites in RPC and confirm the dominant role of the mobile phase in governing the retention and selectivity changes in RPC of nonpolar eluites.

The Associative Properties of Some Amphiphilic Fullerene Derivatives

“…[25,26] The free-energy change for the creation of a cavity in a solvent, ΔG cav , is taken as the work necessary to expand the liquid surface by a quantity equal to the solute molecular surface, A, against the surface tension, γ, of the solvent. Thus, ΔG cav can be calculated [27] by Equation (5). The factor κ corrects γ for the curvature of the cavity.…”

The role of ion pairing in the chromatographic study of propranolol analogues

“…Using such conditions, the log D of other propranolol analogues were determined and the results are shown in Tables III and IV. In the case of PMOS CSP there is no differentiation between the two mobile phase compositions and the log *Papp values are essentially the same. It seems, therefore, that the solvophobic theory might well be of similar importance to explain the physicochemical parameters associated with the retention of propranolol analogues in the same stationary phase, [22]. The change of the mobile phase pH did not show a remarkable discrepancy as would be expected, in the range set examined.…”

“…(6) indicates that in MOPS buffer there is a greater difference in the establishment of homo-energetics of the systems. This means, the solvophobic effect [22] of MOPS is useful for the evaluation of physicochemical parameters in terms of solvent strength. It can be envisaged that the alleged importance of MOPS in lacking an ion-pairing mechanism is fulfilled when compared to phosphate buffer, which can experience it [11].…”

Effective HPLC resolution of [4]heterohelicenium dyes on chiral stationary phases using reversed‐phase eluents

“…With binary organic solvent-water mixtures, logarithmic retention factors decrease linearly with the concentration of the organic solvent. 89 Retention of solutes 1a-c was monitored using MeCN/water mixtures containing 30 mM KPF 6 , where the organic modifier content (volume fraction, /) varied by 5% increments from 65 to 80%. Plots of logarithmic retention (ln k 1 and ln k 2 ) versus eluent composition (/) gave straight lines in all cases (Fig.…”