Simultaneous Determination of Melatonin, l -Tryptophan, and two l -Tryptophan-Derived Esters in Food by HPLC with Graphene Oxide/SiO 2 Nanocomposite as the Adsorbent

In this research, a dispersive solid-phase extraction (dSPE) with graphene oxide@SiO2 (GO@SiO2) nanocomposites as the adsorbent followed by high-performance liquid chromatography analysis was developed for simultaneous determination of melatonin, l-tryptophan, and two l-tryptophan-derived esters in food (black sesame seed (Sesamum indicum L.) was selected in this case). The GO@SiO2 nanocomposite was prepared by one-pot aggregation in aqueous phase with sol-gel technique. The structure and morphology of the GO@SiO2 were characterized by scanning electron microscopy, transmission electron microscopy, Fourier transform-infrared spectroscopy, and X-ray diffraction. The extraction conditions of dSPE including the ratio of material to liquid, adsorption and desorption time, desorption temperature, and desorption solvents were investigated, respectively. The detection limits of the developed method for the analysis of melatonin, l-tryptophan, l-tryptophan methyl ester, and l-tryptophan ethyl ester were achieved below 0.1 μg mL−1. The established method was successfully applied to the analysis of the target analytes in black sesame seed, which provided a simple, low-cost, and sensitive approach for the determination of trace compounds in complex samples.