Determination of anti-obesity drugs in dietary supplements for weight control by capillary electrophoresis

Abstract

Capillary zone electrophoresis (CZE) was developed for simultaneous separation and quantitative analysis of five anti-obesity drugs adulterance in dietary supplements for weight control: phentermine, sibutramine, ephedrine, pseudoephedrine and fenfluramine. The suitable condition were obtained using a 100 mM tris-phosphate buffer at pH 2.5 containing 20% acetonitrile in a fused-silica capillary under applied voltage of 25 kV and temperature of 25 oC. Achieve base line resolution was obtained with Rs > 2.0 and analysis time within 10 min. This method allows the limits of detection (LOD) and limits of quantitation (LOQ) in ranges of 0.10-0.20 and 0.45-1.00 ppm, respectively. Highly linear relationship in concentrations levels of all analytes in a range of LOQ to 50 ppm was obtained with coefficient of determination r2 > 0.999, along with acceptable intraday and interday precision in migration time (tm) and the measured concentration shown by RSD of < 1.0% for tm and < 4.1% for the measured concentration. Satisfactory accuracy was also obtained with recoveries of 96.3-104.9% at LOQ, 95.3-103.7% at 5 ppm and 96.1-104.7% at 30 ppm. Using this method for analysis of real samples extracted by 1:10 ethanol:water with proper dilution, sibutramine was found to be adulterated in four out of eight capsule samples of weight control, with the amount levels up to 2.7% w/w or 6.4 mg/capsule. In addition, a 20 mM ammonium acetate buffer at pH 4 containing 30 to 50% ACN or 40 to 70% MeOH was found to achieve CZE separation of five anti-obesity drugs, that may be used as a volatile buffer in mass spectrometry. Product ions mass spectra of five anti-obesity drugs were also obtained using electrospray ionization-tandem mass spectrometry with a quadrupole-time of fight mass analyzer.