Separation of testosterone metabolites in microsomal incubates using a new capillary electrophoresis assay

A capillary electrophoresis method has been developed to separate the products of liver microsomal testosterone metabolism. The microsomal mixture undergoes liquid-liquid extraction and pre-concentration, and then electrophoretic analysis takes less than 25 min including capillary conditioning steps. The development of the complex background electrolyte (Tris-HCl and borate buffers, sodium dodecyl sulfate, β-cyclodextrin and ethanol) necessary for this separation is described. A z-type capillary flow cell is used to obtain adequate detection sensitivity. The proportion in which the metabolites are produced as determined by this method allows assignment of the relative activity of cytochrome P-450 enzymes in the microsomes. The technique is useful for comparison of activity in normal and abnormal hepatic microsomes.