Novel Potentiometric Sensors for Determination of Melatonin and Oxomemazine in Biological Samples and in Pharmaceutical Formulations

Simple, selective and accurate sensors were developed for the determination of melatonin and oxomemazine in biological samples (urine) and in pharmaceutical preparations. Potentiometric measurements were based on bismus tetraiodate-drug ion-pair as novel electroactive materials incorporating a plasticized PVC membrane with o-nitrophenyl octyl ether or dioctyl phthalate. Each sensor was conditioned for at least two days in 0.1 M drug solution before use. It exhibited fast and stable Nernstian response for melatonin and oxomemazine over the concentration range of 1.0 X 10(-6)-1.0 X 10(-2) M and 1.0 x 10(-5)-1.0 x 10(-2) M, pH range of 3.0-6.5 and 3.5-6.0 for melatonin and oxomemazine sensors, respectively. Results with an average recovery not more than 101\% and a mean standard deviation less than 1.0\% of the nominal were obtained for the four sensors. The sensors showed reasonable selectivity towards investigated drugs in presence of many cations.