Rapid determination of the antimycotic drug flucytosine in human serum by micellar electrokinetic capillary chromatography with direct sample injection.

The rapid determination of flucytosine (5-FC) in human serum by micellar electrokinetic capillary chromatography (MECC) with direct sample injection is discussed. Minute (nanoliter) quantities of patient sera are applied to the beginning of a fused silica capillary filled with a phosphate/borate buffer (pH 9.2) containing 75 mM sodium dodecyl sulfate. Upon application of an electric field along the capillary, endogenous and drug substances are transported toward the cathode and separated into distinct zones that are detected by on-column ultraviolet absorption. Depending on the capillary and instrument used, 5-FC is shown to elute within 2-3.5 min of current application and free of endogenous interferences. 5-FC becomes also well separated from another often coadministered antimycotic drug, amphotericin B. Thus, quantitation of 5-FC is accomplished without any sample pretreatment. MECC data of 60 patient sera produced on two different automated instruments and 5-FC serum levels obtained by an agar-based bioassay are shown to agree well. For MECC, intraday and interday reproducibility data (80 micrograms/ml level) are shown to be < or = 4.5 and < 7%, respectively. Due to short run times and short capillary equilibration time intervals between runs, a sample throughput of 15/h is feasible. Thus, this technology is suitable for rapid determination of 5-FC serum levels, the time requirement for running a complete calibration, two control sera, and several patient samples being approximately 1 h only.