End group selectivity of low-molecular-weight polystyrenes on a carbon-clad zirconia stationary phase in reversed phase HPLC

The separation of isomers of polystyrene oligomers was demonstrated on a carbon-clad zirconia stationary phase in an acetonitrile mobile phase. The carbon-clad zirconia surface gave considerably better resolution of isomers than a C18 surface, and the separation was sensitive to the end group of the oligomer. Oligomers with sec-butyl end groups displayed almost twice as many isomers as the corresponding n-butyl oligomer on the carbon-clad zirconia surface. These additional bands could be explained by the stereochemistry of the sec-butyl end group. In addition, the migration rate of the polystyrene isomers was dependent upon the end group, with n-butyl polystyrenes displaying significantly greater retention on the carbon-clad zirconia stationary phase. In comparison, the selectivity of conventional C18 columns could not discriminate between the n-butyl and sec-butyl end groups.