Determination of Melatonin and Its Metabolites in Biological Fluids and Eggs Using High-Performance Liquid Chromatography with Fluorescence and Quadrupole-Orbitrap High-Resolution Mass Spectrometry

Melatonin is a hormone found in animals, plants, fungi, and bacteria, which can be used as a sleep aid and in the treatment of sleep disorders. Here, a rapid and accurate method was developed for the determination of melatonin in plasma, milk, and egg using high-performance liquid chromatography with fluorimetric detection (HPLC-FLD) and ultra high performance liquid chromatography-quadrupole-orbitrap high-resolution mass spectrometry (UHPLC-Q-Orbitrap HRMS). Sample was extracted with methanol and cleaned by passing through hydrophilic-lipophilic balanced (HLB) solid phase extraction cartridge. The method validation results showed that recovery for melatonin was between 80.3 and 105.1 % with relative standard deviations less than 9.8 %. UHPLC-Q-Orbitrap HRMS was employed as a further means of confirmation to assure accuracy of the results. Limits of detection for melatonin were 0.13 ng g(-1) and 0.14 ng mL(-1) for solid and liquid samples, respectively. Thus, the proposed method can be applied to detect melatonin in milk, plasma, and egg samples. Meanwhile, the metabolites of melatonin were identified using Q-Orbitrap HRMS. The approach identified five metabolites; among them, a novel metabolite, named mono-oxygenation-demethylation-melatonin, was found in plasma.