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

Abstract

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

“…The calibration curve is highly linear in the 0.1-10 µg/mL concentration range, with a correlation coefficient (r) of 0.999 (Table 1). In a previous report using LC/TOF-MS [10], the LOD and LOQ were 0.25 and 0.5 µg/mL, respectively, indicating that the present analysis method is more sensitive. Furthermore, the LC/FL method is more advantageous than the LC/TOF-MS method, because an LC/FL instrument is widely used in the field of analytical chemistry, and is less susceptible to matrix effects, which are generally a problem with MS detection.…”

“…Dietary supplements claiming to contain synephrine made in Japan (domestic), the United States, and China were used as target samples, which were extracted according to a previously reported method [10]. Briefly, samples in tablet form were crushed into powders, while the contents were removed from capsules.…”

“…FMOC derivatives were prepared according to a previously reported method [10]. Briefly, 15 mM FMOC/acetonitrile solution (250 μL, the derivatization reagent) and 50 mM borate buffer solution (50 μL) were added to a synephrine standard solution or sample solution (250 μL).…”

“…1-A, B), with the l-isomer predominantly present in natural products [7]; this enantiomer acts on adrenergic receptors 10-100-times more strongly than the denantiomer [8,9]. Previous studies have confirmed that some health foods labeled as naturally derived (i.e., containing the l-isomer) contain high percentages of the d-isomer [10]. As one of the reasons, we thought that isomerization is caused by heating during manufacturing or that the description was violated.…”

“…In this study, we investigated chromatographically separating and isolating each synephrine enantiomer from a commercially available racemate. Although we previously reported a liquid chromatography/time-offlight mass spectrometry (LC/TOF-MS) method for analyzing synephrine enantiomers [10], in this study, we investigated the more sensitive and widely used liquid chromatography-fluorescence detection (LC/FL) method, and used it to determine synephrine enantiomers in commercially available dietary supplements in a highly sensitive manner.…”