GAS-CHROMATOGRAPHIC RETENTION BEHAVIOR OF DIBENZOTHIOPHENE DERIVATIVES ON A SMECTIC LIQUID-CRYSTALLINE POLYSILOXANE STATIONARY PHASE

The gas chromatographic retention behaviour, on a smectic liquid crystalline polysiloxane stationary phase, of methyldibenzothiophenes and eighteen C2-dibenzothiophenes (sixteen dimethyldibenzothiophenes and two ethyldibenzothiophenes), out of twenty possible compounds, was investigated. The retention, in addition to vapour pressure and polarity, was greatly influenced by the molecular geometry of the solutes. The major factor affecting this behaviour was the length to breadth ratio (L/B). The elution order of the dimethyldibenzothiophenes was fairly well correlated with L/B values: Roughly, the lower the L/B values, the earlier the dimethyldibenzothiophenes were eluted. However, the solute molecular shape, although of less importance, was also a significant retention-affecting factor, having the contrary effect to L/B values on the elution order. Arc-like molecules (dibenzothiophenes) with groups attached to the outer curved side (i.e., in positions 3 and 4) were retained longer than predicted by L/B values. In contrast, isomers conforming to the arc-like arrangement (i.e., with substituents in positions 1 and 2) were less retained than predicted. The application of these identifications to a crude oil sample is described.