Comparison of Analytical Methods for the Rapid Determination of Melatonin in Food Supplements

Melatonin is a hormone produced by the pineal gland and extra-pineal tissues with chronobiotic effects that can alter the circadian rhythms, among other health benefits. This study intended to compare two different methods, high-performance liquid chromatography coupled to a variable wavelength detector plus a fluorescence detector (HPLC-VWD-FLD) and constant-wavelength synchronous spectrofluorimetry, to determine melatonin in food supplements. HPLC-MS/MS was used as a confirmatory technique. The data showed that both analytical methodologies were valid for the determination of melatonin with correlation between the datasets obtained (99% confidence level). Constant-wavelength synchronous spectrofluorimetry is a fast, simple, and economical method that can be used for a rapid and precise determination of melatonin in supplements, in the absence of other compounds that could interfere in the analysis. On the other hand, the HPLC-VWD-FLD method showed to be more suitable for the determination of melatonin in complex samples because of its high sensitivity and separation efficiency. Finally, all supplements analyzed from the Spanish market comply with the melatonin content declared on the label and with the claim “contributes to the alleviation of subjective feelings of the jet lag of jet lag” (0.5 mg/day). Also, 7 out of 10 complain about the claim “contributes to the reduction of time taken to fall asleep” (1 mg/day).