COLORIMETRIC AND SPECTROFLUOROMETRIC METHODS FOR THE DETERMINATION OFMELATONIN IN TABLETS AND SERUM

Two sensitive and accurate colorimetric and spectrofluorimetric method s are presented for the determination of melatonin in tablets and seru m. The first method utilizes the reactions of p-dimethylaminobenzaldeh yde in hydrochloric acid (van Urk reagent)-ferric chloride in sulphuri c acid(Salkowski reagent)mixture. The blue color of the resulting reac tion product Is measured at 630 The second method is based on the reac tion of melatonin with o-phthalaldehyde in acid medium which yields hi ghly fluorescent condensation product that is measured at 465 nm as em ission wavelength, using excitation wavelength at 355 run. No interfer ence was observed from tableting additives, and the applicability of t he methods was examined by analysing tablets containing melatonin(sing le and combined with pyridoxine). Mean percentage recoveries from tabl ets were found to be 99.9+/-0.31 for single and 100.5+/-0.15 for combi ned tablets using colorimetric method, while by applying spectrofluori metric method the recoveries were found to be 100.6+/-0.41 for single and 100.2+/-0.39 for combined tablets. Furthermore. the proposed metho ds were extended to the in-vitro determination of melatonin in serum. The detection limits are 0.27 ug ml(-1) for colorimetric method and 0. 00035 ug ml(-1) for spectrofluorimetric method.