Improvement of Gas Chromatographic Performance of Cyclic Siloxane Bonded Phases by Incorporation of n-Alkyl Groups

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Abstract
Cyclic siloxane-based silica columns of high retention capacity for light hydrocarbons were prepared by incorporation of octyl and octadecyl groups on the siloxane skeleton. Spectroscopic studies revealed the presence of the alkyl groups on the silica surface, which results in high surface coverage of the packing materials. The retention characteristics of the columns are significantly higher than those of cyclic siloxane phases due to their high surface coverage and better solute−stationary phase interactions. In agreement with previous data for micropacked columns, the H vs ū curves, on passing through the optimum region, remained substantially constant at high linear gas velocities, indicating their usefulness for fast analysis of light hydrocarbons at high flow rates without any appreciable loss in column performance. Presumably due to greater availability of the bonded alkyl groups for interactions, a 10-component mixture of C1−C4 saturated and unsaturated hydrocarbons was sufficiently separated on the hexamethylcyclotrisiloxane−octadecylsilyl phase compared to the conventional octadecyldimethylsilyl phase, irrespective of the high carbon content of the latter.