Retention characteristics and selected applications of cyclic siloxane-based octadecylsilyl bonded phases in reversed-phase high-performance liquid chromatography

Hexamethylcyclotrisiloxane- and octaphenylcyclotetrasiloxane-based octadecyl bonded phases are prepared and evaluated for liquid chromatographic separation of various compounds. As revealed by the retention data of the selected solutes, the hexamethylcyclotrisiloxane-octadecyl phase exhibits better chromatographic performance than octaphenylcyclotetrasiloxane-octadecyl phase presumably due to greater accessibility of the bonded alkyl groups on the siloxane skeleton for interactions. The peak asymmetry values showed that solute retention on the hexamethylcyclotrisiloxane-octadecyl phase is essentially controlled by dispersive interactions. The retention characteristics of the cyclicsiloxane-based phases were compared to those obtained on a commercial C-18 column and an octadecyl phase synthesized through a silanization-hydrosilation addition process, While the two phases gave baseline separation of polycyclic aromatic hydrocarbons and barbiturates, the hexamethylcyclotrisiloxane-octadecyl phase allowed fast and efficient separation of a four-component standard mixture of tricyclic antidepressants.