Radiation immobilization of poly(methyloctylsiloxane) on silica for use inHPLC: a uniform layer model

Poly(methyloctylsiloxane) (PMOS) was sorbed into the pores of HPLC silica b y a solvent evaporation procedure, then irradiated with gamma rays from a c obalt-60 source to absorbed doses in the range from 0 to 200 kGy (1Gy=1J kg (-1)). Non-irradiated and irradiated samples were characterized by solvent extraction, specific surface area determination, infrared spectroscopy and reversed-phase column performance. Solvent extraction data reveal that abou t 40% of the PMOS is not extractable prior to irradiation and this increase s to about 75% with radiation doses of 50 kGy or higher. Column performance was improved by the radiation treatment, reaching a maximum efficiency in the dose range of 80-140 kGy while the peak symmetry changed from As=1.7 to 1.1. The improvement is attributed to the increased mass of polymer immobi lized by the radiation treatment and to a more uniform distribution of the immobilized polymer in the silica pore system. A multi-layer stationary-pha se model is presented in which the first layer consists of an adsorbed mono layer of PMOS and the second layer is immobilzed by gamma radiation. (C) 19 99 Elsevier Science B.V. All rights reserved.