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 pr operties of a cyanopropylsiloxane-bonded, silica-based sorbent with me thanol, acetonitrile, tetrahydrofuran, and isopropanol in water as mob ile phases. The system constants over the composition range 1 to 50 % (v/v) organic solvent indicate that retention occurs because of the re lative ease of cavity formation in the solvated stationary phase compa red to the same process in the predominantly aqueous mobile phase as w ell 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 inte ractions result in reduced retention. Graphing the system constants as a function of mobile phase composition provides a simple mechanism fo r interpreting the change in capacity of the chromatographic system fo r retention in terms of changes in the relative weighting of fundament al intermolecular interactions. A comparison is also made with the ret ention properties of an octadecylsiloxane-bonded , silica-based sorben t with 30 % (v/v) methanol in water as the mobile phase and the extrac tion characteristics of a porous polymer sorbent with 1 %(v/v) methano l, acetonitrile, tetrahydrofuran, and isopropanol in water as the samp le processing solvent. Changes in sorbent selectivity due to selective up take of the processing solvent are much smaller for the cyanopropy lsiloxane-bonded sorbent than the results found for a porous polymer s orbent.