Separation of steroid isomers using a liquid crystalline polysiloxane stationary phase in capillary supercritical fluid chromatography

A liquid crystalline biphenylcarboxylate ester polysiloxane stationary phase was used to study the effect of solute structure on retention for the separation of isomeric steroids in capillary supercritical fluid chromatography. It was determined that theretention mechanism is related to solute molecular shape rather than to properties such as volatility or polarity. The elution order of isomeric androstanes and estrogens could be correlated with the planarity of molecules: more‐planar molecules were retained longer on the column. The resolution of steroid isomers was improved significantly using the liquid crystalline stationary phase when compared with results obtained using other stationary phases.