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 μg/mL. The limit of detection (LOD, S/N = 3) and the limit of quantification (LOQ, S/N > 10) were 0.25 μg/mL and 0.5 μg/mL, respectively. The intra-day and inter-day accuracy of synephrine enantiomers at the LOQ level (0.5 μg/mL), the intermediate concentration level (10 μg/mL), and the high concentration level (50 μg/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.

A method for the simultaneous determination of 13 slimming drugs in dietary supplements by liquid chromatography/time-of-flight mass spectrometry was developed and applied to real-time surveys of imported health supplements. The target compounds were mutually well separated on a reversed-phase LC Shodex ODP2-HP 2D column using a combination of step-wise and linear gradient elution of a mixed mobile phase solution of ammonium formate buffer, methanol, and formic acid. The detection limits were in the range 1-50 ng/mL, and the lower limits of quantification were 2-100 ng/mL. The average recoveries of the 13 types of pharmaceutical ingredients in the diet supplements were 93-110%, and the RSD was within 7.1%. Applying the developed method to the survey of imported dietary supplements revealed that 32 out of the 39 Chinese products tested contained pharmaceutical ingredients such as sibutramine. On the other hand, out of 30 US products, synephrine was detected in 26 specimens, and yohimbine was detected in 8 specimens. These results proved that a number of products were contaminated by drugs, which was considered to be intentional. The developed method is applicable for the survey of imported health supplements suspected to be contaminated with pharmaceutical ingredients.