IMPROVEMENT OF GAS-CHROMATOGRAPHIC PERFORMANCE OF CYELIC SILOXANE BONDED PHASES BY INCORPORATION OF N-ALKYL QROUPS

Cyclic siloxane-based silica columns of high retention capacity for li ght hydrocarbons were prepared by incorporation of octyl and octadecyl groups on the siloxane skeleton, Spectroscopic studies revealed the p resence of the allyl groups on the silica surface, which results in hi gh surface coverage of the packing materials, The retention characteri stics of the columns are significantly higher than those of cyclic sil oxane phases due to their high surface coverage and better solute-stat ionary phase interactions. in agreement with previous data for micropa cked columns, the H vs u curves, on passing through the optimum region , remained substantially constant at high linear gas velocities, indic ating their usefulness for fast analysis of light hydrocarbons at high now rates without any appreciable loss in column performance. Presuma bly due to greater availability of the bonded alkyl groups for interac tions, a 10-component mixture of C-1-C-4 saturated and unsaturated hyd rocarbons was sufficiently separated on the hexamethylcyclotrisiloxane -octadecylsilyl phase compared to the conventional octadecyldimethylsi lyl phase, irrespective of the high carbon content of the latter.