A Sensitive Chiral Analytical Liquid Chromatography/Fluorescence Detection Method for Synephrine in Dietary Supplements

A method for isolating each enantiomer of synephrine from the racemate using chiral chromatography was investigated, and a simple and highly sensitive analytical method for determining synephrine enantiomers in commercial dietary supplements was constructed using chiral liquid chromatography-fluorescence detection (LC/FL). For isolating each enantiomer, synephrine was derivatized with the 9-fluorenylmethyl chloroformate (FMOC-Cl) and separated by chiral LC after removing excess FMOC-Cl by solid-phase extraction (OASIS MCX cartridge). Deprotection was performed with piperidine, with excess piperidine removed using an HLB cartridge. A sample solution extracted from a dietary supplement was cleaned by solidphase dispersive extraction with MCX, after which each enantiomer was derivatized using FMOC-Cl. Chiral LC was performed using a TCI Chiral MB-S column with a 75:25 mixture of 50 mM aqueous phosphoric acid solution/acetonitrile as the mobile phase. The limit of detection and limit of quantification values of 0.03 and 0.1 mu g/mL, respectively, were recorded, along with a repeatability of < 15%, an intermediate precision of < 20%, and an accuracy of > 80%. Analysis of 17 commercial dietary supplements revealed that some exhibited enantiomeric excesses of less than 70% for the l-isomer, which suggests that partial racemization occurred in the manufacturing process. The developed method can be used to clarify the synephrine-isomerization mechanism in the food-hygiene field.