Preparation and characterization of indole grafted membranes for the isolation of physiologically important melatonin

Melatonin (5-methoxy-N-acetyltryptamine) is an important hormone that plays a role in regulating the neuroendocrine system, and in the regulation of the circadian sleep-wake cycle. It is known that melatonin is very effective various diseases such as cancer, depressive syndrome and immune system and also that melatonin has broad usage in cosmetics as moisturizer, lipoidozis preventive, regenerative, anti-wrinkle. Due to their common usage in medicine and cosmetic industry, extraction and determination of melatonin with high purity and selectively using rapid and low-cost method from natural sources, such as high plants, have great importance. In the last 20 years, intensive researches about solid phase extraction field have guided to develop new materials for selective extraction of analyte from several matrixes. In this study, preparation and characterization of polymeric membranes which can be used as SPE cartridge for the extraction and determination of melatonin in complex biological matrices were aimed. For this purpose, p(HEMA) membranes were prepared with UV-initiated photopolymerization of 2-hydroxyethylmethacrylate. The membrane was then grafted with L-tyrptophane and used for the extraction of melatonin via adsorption. Melatonin adsorption onto the membrane from aqueous solutions was studied with different amounts of melatonin at different temperature and time in a batch system. The maximum melatonin adsorption capacity of the L-Trp grafted pHEMA membranes was found to be 36.58 mg/g. 100% of the adsorbed melatonin was desorbed by using triethylamine:methanol mixture (1:9) as desorption agent. It was demonstrated that the prepared L-Trp grafted pHEMA membranes could be repeatedly applied to extraction of melatonin before chromatographic analysis.