INFLUENCE OF SOLVENT EFFECTS ON THE BREAKTHROUGH VOLUME IN SOLID-PHASE EXTRACTION USING POROUS POLYMER PARTICLE-LOADED MEMBRANES

A general dependence of the breakthrough volume in solid-phase extraction, using a porous polymer particle-loaded membrane on the selection of the organic solvent added to water at the 1% (v/v) level to promote acceptable and even how through the membrane is demonstrated. The selective sorption of the organic solvent by the polymer changes the stationary-phase volume and the system selectivity, resulting in changes in up to an order of magnitude in the breakthrough volume when either methanol, propan-1-ol, tetrahydrofuran, or acetonitrile are used as the organic-solvent modifier. A solvation parameter model is used to characterize the changes in selectivity of the sampling system incorporating the different solvent modifiers. Retention by the solvated porous polymer sorbent occurs because of the relative ease of cavity formation in the sorbent compared to the sample solvent while all polar interactions, especially hydrogen-bond interactions, tend to reduce retention by the sorbent, and result in smaller breakthrough volumes. In determining the optimum solvent to obtain an adequate breakthrough volume, the solute size is as important as the capacity of the solute for polar interactions. All relevant factors are taken into account through the solvation parameter model which allows the prediction of breakthrough volumes with different sample co-solvents with adequate accuracy for practical applications.