Stereoselective determination of clenbuterol in human urine by capillary electrophoresis.

The effectiveness of capillary electrophoresis (CE) in the field of stereoselective determination of drugs in biological matrices is demonstrated by analyzing clenbuterol in human urine. Due to the very low therapeutical doses of 20-40 microg per day the total concentrations in urine are 1-10 ng/ml. The sample was extracted with hexane-tert.-butyl methyl ether (99.5:0.5). The reconstituted sample was injected electrokinetically (50 s, 10 kV). Using phosphate buffer, pH 3.3 and hydroxyethyl-beta-cyclodextrin as chiral selector the total analysis time was below 15 min. The limit of determination was estimated as 0.5 ng/ml per enantiomer. S-(-)-Bupranolol was used as internal standard. Both precision and accuracy of the method were within the limits for biological samples. The application to human urine from patients having received therapeutical doses showed a slightly predominant excretion of the (+)-enantiomer to the (-)-enantiomer.