Determination of finasteride and its metabolite in urine by dispersive liquid-liquid microextraction combined with field-enhanced sample stacking and sweeping.

The on-line preconcentration technique of field-enhanced sample stacking and sweeping (FESS-sweeping) are combined with dispersive liquid-liquid microextraction (DLLME) to monitor the concentrations of finasteride, which is used in the treatment of androgenetic alopecia, and its metabolite, finasteride carboxylic acid (M3), in urine samples. DLLME is used to concentrate and eliminate the interferences of urine samples and uses chloroform as an extracting solvent and acetonitrile as a disperser solvent. A high conductivity buffer (HCB) was introduced into capillary and then sample plug (90.7% capillary length) was injected into capillary. After applying voltage, the sodium dodecyl sulfate (SDS) swept the analytes from the low conductivity sample solution into HCB. The analytes were concentrated on the field-enhanced sample stacking boundary. The limit of detection for the analytes is 20 ng mL-1. The sensitivity enrichment of finasteride and M3 are 362-fold and 480-fold, respectively, compared with the conventional MEKC method. The on-line preconcentration technique of field-enhanced sample stacking and sweeping possess good selectivity because the endogenous steroid did not interfere the detection of finasteride and M3. The analytical technique is applied to investigate the concentrations in urine samples from patients who have been administered finasteride for the treatment of androgenetic alopecia; the amount of M3 detected in 12 h was 72.69 ± 4.18 μg.