Simultaneous determination of sibutramine and N-di-desmethylsibutramine in dietary supplements for weight control by HPLC-ESI-MS

A high-performance liquid chromatographic method, coupled with UV detection and electrospray ionization mass spectrometry (HPLC-UV-ESI-MS), is developed for the simultaneous determination of the illegal additives sibutramine and its metabolite N-di-desmethylsibutramine in dietary supplements for weight control. The separation is achieved on a Spherisorb C8 reversed-phase column, employing acetonitrile and an aqueous 0.2% formic acid solution containing 20mM ammonium acetate as mobile phases in a gradient mode. UV detection is used for quantitation at a wavelength of 223 nm. Identification of target compounds is completed by ESI-MS using selected ion recording at m/z 280 for sibutramine and m/z 252 for N-di-desmethylsibutramine. Calibration curves are linear over the range of 0.025-1.0 mg/mL for sibutramine and N-di-desmethylsibutramine. Correlation coefficients are better than 0.9990. The intra- and inter-day precision and accuracy for sibutramine and N-didesmethylsibutramine are acceptable. The method is successfully applied to the analysis of natural dietary supplement samples.