INFLUENCE OF SOLVENT EFFECTS ON RETENTION IN REVERSED-PHASE LIQUID-CHROMATOGRAPHY AND SOLID-PHASE EXTRACTION USING A CYANOPROPYLSILOXANE-BONDED, SILICA-BASED SORBENT

The solvation parameter model is used to characterize the retention properties of a cyanopropylsiloxane-bonded, silica-based sorbent with methanol, acetonitrile, tetrahydrofuran, and isopropanol in water as mobile phases. The system constants over the composition range 1 to 50 % (v/v) organic solvent indicate that retention occurs because of the relative ease of cavity formation in the solvated stationary phase compared to the same process in the predominantly aqueous mobile phase as well as from more favorable stationary phase interactions with solutes containing pi- and n-electrons. The capacity of the solute for dipole-type interactions is not important whereas all hydrogen-bond-type interactions result in reduced retention. Graphing the system constants as a function of mobile phase composition provides a simple mechanism for interpreting the change in capacity of the chromatographic system for retention in terms of changes in the relative weighting of fundamental intermolecular interactions. A comparison is also made with the retention properties of an octadecylsiloxane-bonded , silica-based sorbent with 30 % (v/v) methanol in water as the mobile phase and the extraction characteristics of a porous polymer sorbent with 1 %(v/v) methanol, acetonitrile, tetrahydrofuran, and isopropanol in water as the sample processing solvent. Changes in sorbent selectivity due to selective up take of the processing solvent are much smaller for the cyanopropylsiloxane-bonded sorbent than the results found for a porous polymer sorbent.