Anionic-zwitterionic mixed micelles in the micellar electrokinetic separation of clinically relevant steroids on a fused-silica capillary

The structural similarities of different clinically relevant steroids make their routine determination in biological samples an analytical challenge. Determination of steroidal hormones in urine and serum is of great interest in clinical endocrinology. A large number of disorders is associated with hypo- or hypersecretion of one or more steroids, for example, Addison's disease, Cushing's syndrome, hirsutism and virilism, adrenal adenomas, hypertension, congenital adrenal hyperplasia etc. A SDS/SB3-12 mixed micellar system was used to achieve baseline separation of eight steroids in less than 10 min. Five different zwitterionic surfactants were evaluated at different concentrations, pH and temperature conditions. The SB3-12/SDS mixed micellar system gave highest resolution and precision. No significant capillary wall interaction or coating effects were observed with the zwitterionic surfactants as is evident from the reproducible migration times (relative standard deviation ≤2%). A detection limit of 1-5 μg/ml was obtained for pure standards.