Flow-injection amperometric determination of adrenalin, melatonin, and Cortisol on the electrode modified by gold - palladium binary system and Nation film

Pharmaceuticals containing steroid hormones and their synthetic analogues are widely used in medicine. Accurate determination of the hormone content in biomedical objects is an urgent problem in modem analytical chemistry. A method for the selective and highly sensitive amperometric determination of adrenaline, melatonin, and cortisol in a flow-injection system has been developed. A scheme of a two-detector flow-injection system was proposed for the simultaneous determination of the adrenaline, melatonin, and cortisol content. Screen-printed carbon electrodes (SPE) with one or two working electrodes modified by gold-palladium binary system, which exhibited catalytic activity upon electrooxidation of organic compounds under study were used as detectors. A high sensitivity of the determination is attributed to the catalytic properties of the metal modifier: the transition between the metal and binary system leads to an increase in the catalytic current of hormones oxidation. The selectivity of the adrenaline determination in the presence of melatonin and cortisol is provided by the difference in the potentials of hormone oxidation at the developed electrode. For the selective determination of melatonin and cortisol the surface of the working electrode was modified by the Nation film. The potential difference between the oxidation peaks of adrenaline, melatonin and cortisol on the modified electrode was 300 mV. The proposed method was tested in analysis of real urine samples. The flow-injection scheme was supplemented with a dialyzer and a chromatographic mini-column to eliminate the interfering effect of electrophilic compounds. The linear logarithmic dependence of the analytical signal on the concentration of adrenaline, melatonin and cortisol is observed in the range from 5.0 x 10^-10 to 5.0 x 10^-3 M, from 5.0 x 10^-11 to 5.0 x 10^-3 M, and from 5.0 x 10^-12 to 5.0 x 10^-3 M, respectively. Amperometric determination of hormones in a flow-injection system leads to an increase in the productivity of analysis, decrease in the sample consumption and provides for automation of the process.

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