DETERMINATION OF MENADIONE BASED ON ITS POLAROGRAPHIC CATALYTIC WAVE IN THE PRESENCE OF POTASSIUM IODINATE

A method for the determination of menadione was proposed. In 0.2 mol/L HOAc–NaOAc (pH 4.7) buffer solution containing 4.0 × 10-3 mol/L KIO3, menadione yields a well-defined polarographic catalytic wave with a peak potential of -0.95 V (vs. SCE). The second order derivative peak current is linearly proportional to the menadione concentration in the range of 4.0 × 10-8–2.0 × 10-6mol/L with the correlation coefficient of 0.999 (n = 8). The detection limit is 2.0 × 10-8mol/L. The sensitivity of the catalytic wave is 10 times higher than that of the corresponding reduction wave in the absence of KIO3. The proposed method was used to directly determine the menadione contents in clinical injections in good agreement with the labeled amount without preseparation. The mechanism of polarographic catalytic wave of menadione was discussed. The polarographic reduction wave of menadione itself in the acetate buffer solution is ascribed to that the carbonyl group of menadione is reduced in consecutive two electrons and two protons addition to hydroquinone via semiquinone (quinone-hydroquinone) free radical intermediates. In the presence of KIO3, the carbonyl group of menadione is chemically regenerated due to oxidation of semiquinone free radical intermediates by KIO3 and a series of its derived species formed during six-electron successive reduction process. The maximum current of the first charge transfer is enhanced, and the second electroreduction step of menadione is inhibited.