Determination of melatonin in galenic preparations by LC and voltammetry

The amount of melatonin in galenic tablets was determined by means of two feasible and accurate analytical methods. The high performance liquid chromatography (HPLC) with ultraviolet detection at 223 nm used a C(18) reversed-phase column; the linear scan voltammetric procedure (LSV) employs a pH 3.0 phosphate buffer as the supporting electrolyte for the oxidation process of melatonin, which has a current intensity maximum at +850 mV. The two methods gave satisfactory results in terms of precision and accuracy. In fact, the data of repeatability and intermediate precision expressed as percentage relative standard deviations (RSD%) were < or =2.8 and the accuracy values, resulting from recovery experiments, were between 99.0 and 101.3%. Both methods are suitable for quality control of melatonin in galenic preparations; the LSV procedure is more rapid, the HPLC method is more sensitive and more precise.