Liquid chromatographic retention behaviour and separation of chlorophenols on a β-cyclodextrin bonded-phase column. Part III. Diaromatic chlorophenols

Abstract

The liquid chromatographic retention behaviour of 16 diaromatic phenols and chlorophenols (PCB metabolic analogues) on a β-cyclodextrin bonded-phase column was investigated with respect to mobile-phase composition, pH, temperature, and ionic strength. The mechanistic aspects of retention of these compounds on the β-cyclodextrin column were studied and compared to other reversed-phase columns. Comparison is also made to the liquid chromatographic retention behaviour and separation of monoaromatic chlorophenols on the same column. The size, shape, and spatial geometry of each substrate appears to affect retention and selectivity. Most of the evidence suggests that inclusion complex formation, which involves hydrophobic interactions with the interior of the cavity and/or van der Waals interactions of the chlorine substituents with the backbone of the cavity, provides the physical basis for the resolution of these positional isomers. Under certain chromatographic conditions, however, it appears that, for certain congeners, all or part of the molecule is excluded from the cyclodextrin cavity; in such cases a normal-phase or mixed chromatographic mechanism is postulated based on the interaction of the substrates with the secondary hydroxyls on the periphery of the cyclodextrin moieties. The gradient–elution separation of 14 out of 16 of this type of compound on a single chromatogram is also reported and discussed. Keywords: biphenylols, chlorobiphenylols, biphenyldiols, liquid chromatographic retention behaviour, gradient-elution separation, β-cyclodextrin bonded-phase column.