Detection of hypoglycemic drugs in human urine using micellar electrokinetic chromatography

Micellar electrokinetic chromatography (MEKC) is evaluated as a potential analytical method for the separation and detection of a series of sulfonylurea drugs used in the treatment of hyperglycemia. These drugs are often surreptitiously abused, producing extremely low blood glucose levels and symptoms indistinguishable from those associated with an insulin-secreting tumor. Separation buffer containing 50 mM sodium dodecyl sulfate (SDS) was found to be adequate for the MEKC separation of the third generation drugs (glipizide and glyburide) but not the second generation drugs (acetohexamide chlorpropamide, tolazamide, and tolbutamide). At a pH of 8.5 in the presence of 20 mM borate/20 mM phosphate and 150 mM SDS, all seven components were adequately resolved with an analysis time of 17 min. Altering the concentration of the buffering components to either 5 mM borate/5 mM phosphate or 40 mM borate alone reduced the analysis time to less than 10 min with no observable loss in resolution. A series of other micelle-forming surfactants were evaluated, and only sodium cholate provided an improvement over the SDS-based system. Optimal separation was obtained with 75 mM sodium cholate and led to complete analysis with baseline resolution of all seven components in less than 8 min. These conditions were shown to be adequate for the detection of the hypoglycemic drugs spiked into normal urine and in patients taking these drugs. The precision associated with nine consecutive injections of six samples (n = 54) was found to be acceptable with percent coefficient of variance for absolute migration times (MTabs) for all peaks averaging 0.89 with peak area and peak height being 8.49 and 8.26, respectively. The between-sample precision was found to average 0.92% for MTabs and 8.56% and 8.45%, respectively, for the relative peak area and peak height. With a detection limit for the drugs in urine (following extraction) in the 50 ng/mL range, the potential exists for an MEKC-based assay for the detection of sulfonylurea drugs in urine.