SummaryThe influence of acetonitrile, methanol and isopropanol as retention selectivity modifiers in reversed phase liquid chromatography on a poly(styrene-divinylbenzene) macroporous polymer sorbent (PLRP-S) is evaluated using the solvation parameter model. Retention results from a combination of adsorption and partitioning and is influenced by the equilibrium absorption of organic solvent by the polymer from the mobile phase. The sorption of solutes is dominated by the ease of cavity formation in or on the solvated sorbent, with a small contribution from lone pair-lone pair electron interactions. All polar interactions, such as dipole-type and hydrogenbond formation, are more favorable in the mobile phase and reduce retention. Changes in the uptake of organic solvent from the mobile phase affect kinetic properties of the column such as band broadening and porosity as well as retention. The PLRP-S solvated sorbent is suitable for solid-phase extraction and is more retentive than typical silica-based, bonded phase sorbents for extraction from water. As a surrogate system for estimating solute lipophilicity and biological activity through retention-property correlations it provides a poor fit for hydrogen-bond acid solutes and is too dipolar/polarizable to fit some models.
The influence of temperature on retention and selectivity in reversed-phase liquid chromatography using a porous organic polymer stationary phase is quantitatively characterized using the solvation parameter model. The predominant influence of increasing temperature (20-60 °C) is to decrease the relative difference in the ease of cavity formation between the aqueous mobile phase and solvated sorbent and to decrease the hydrogen-bond acidity of the aqueous mobile phase, with other polar interactions affected to a lesser extent. Temperature variation and composition variation produce similar trends in retention, but within the easily accessible range for both variables, the capacity to change retention is much greater for composition variation than temperature variation. Temperature variation is a useful parameter for fine tuning an isocratic separation with an outcome that is easily predicted using the solvation parameter model.
A new approach for the prediction of retention in reversed-phase liquid chromatography using ternary mobile phase compositions is presented. The solvation parameter model is used to generate system constants characteristic of the capability of the chromatographic system for defined solvent-solvent and solute-solvent interactions. A mixture-design approach is then used to construct system surfaces for each system constant over all mobile phase compositions. These surfaces are smooth and devoid of irregular features. Models derived from these surfaces allowed us to predict the retention of a varied group of 36 solutes on a porous polymer sorbent, PLRP-S 300, at a methanol-acetonitrile-water composition not included in the data used to construct the system surfaces. The accuracy of the predicted retention factors was similar to that obtained by fitting the solvation parameter model to the same experimental data.
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