Enantioselective Determination of Synephrine in Health Food Products by Liquid Chromatography/Time-of-Flight Mass Spectrometry

An enantioselective analytical method for the determination of synephrine, an ingredient in health food, by liquid chromatography/time-of-flight mass spectrometry (LC/TOF-MS) was developed. By derivatizing synephrine with FMOC and using TCI Chiral MB-S as the chiral column, FMOC-synephrine enantiomers were well separated. The electrospray ionization (ESI) negative mode was adopted for TOF-MS measurement. Good linearity (r > 0.999) was obtained in the concentration range of 0.5 to 50 mu g/mL. The limit of detection (LOD, S/N = 3) and the limit of quantification (LOQ, S/N > 10) were 0.25 mu g/mL and 0.5 mu g/mL, respectively. The intra-day and inter-day accuracy of synephrine enantiomers at the LOQ level (0.5 mu g/mL), the intermediate concentration level (10 mu g/mL), and the high concentration level (50 mu g/mL) ranged from 90.0 to 107.4%. The intra-day and inter-day precisions were <= 9.24% and <= 10.63%, respectively. As a result of analyzing synephrine-containing health foods using this method, approximately half of the products showed high optical purity with 80-100% enantiomeric excess of the l-isomer. In contrast, nearly 20% of the products contained racemate with 0-50% enantiomeric excess, and variations in optical purity were observed for the products. It was speculated that the l-isomer could be converted into the d-isomer during the manufacturing process.