Examining the origin of melatonin from a "natural" source by isotope ratio mass spectrometry with liquid chromatographic introduction

The isotopic abundance of 13C often can be used to differentiate between natural and synthetic sources of a given material. These differences are small, and a multicollector isotope ratio mass spectrometer (IRMS) is required. In our laboratory, we developed a liquid chromatographic (LC) introduction system that enables continuous monitoring of 13C isotope ratios for nonvolatile materials without derivatization. The particular question being asked here relates to the source of melatonin in products sold in health food stores. Melatonin is a pineal hormone and its natural source is the brain's pineal gland. The increasing frequency of "mad cow disease" points to a potential danger if bovine pineals were really the source of melatonin in health food preparations. Using a system in which an LC system is interfaced to an IRMS, we evaluated the origin of one melatonin product labeled as being of bovine pineal origin by comparing its 13C/ 12C ratio to those of pure, synthetic melatonin and 2 other melatonin products labeled as being of synthetic origin. We did not find significant differences among the isotope ratios of these 4 melatonin sources. The finding suggests that bovine pineal melatonin is not present in the product labeled as "natural." The work demonstrates the ability of an apparatus combining LC and IRMS to provide detailed information regarding economic adulteration or fraud