VARIATION OF SELECTIVITY AMONG THE POLY(SILOXANE) STATIONARY PHASES FOR GAS-CHROMATOGRAPHY

The solvation parameter model is used to characterize the solvent prop erties of 12 poly(siloxane) stationary phases of varied structure. Sel ectivity differences are explained in terms of differences in the cohe sive energy of the solvents and their capacity for dispersion, dipole- type, hydrogen bonding, and electron pair complexation interactions. N one of the poly(siloxane) stationary phases exhibited significant hydr ogen-bond acid character. Principal component analysis indicates that replacing a methyl group by a phenyl group in the poly(siloxane) backb one predominantly produces incremental increases in the capacity of th e stationary phase for dipole-type interactions (up to about 50 mol% p henyl groups with only small changes at higher phenyl composition). Th e poly(methylphenylsiloxanes), however, only span a small sector of th e selectivity space and provide limited opportunities for selectivity optimization. OV-275 and QF-1 are identified as important phases with unique characteristics-OV-275 because of its high cohesive energy and great capacity for dipole-type and solvent hydrogen-bond base interact ions and QF-1 because of its unusually small hydrogen-bond basicity fo r a phase with an intermediate capacity for dipole-type interactions a s well as a low capacity for n- and pi-electron complexation interacti ons. From these studies it is possible to speculate on the needs for n ew phases to explore the full selectivity potential of gas chromatogra phy and to address the issue of temperature and its relationship to se lectivity. (C) 1995 John Wiley & Sons, Inc.