Study on the Polarographic Catalytic Wave of Vitamin P in the Presence of Persulfate and Its Application

Abstract

The polarographic catalytic wave of vitamin P in the presence of persulfate was studied by linear potential scan polarography and cyclic voltammetry. Vitamin P yielded a single reduction wave in acidic aqueous solution, which was ascribed to a 2e−, 2H+ reduction of the carbonyl group in the C-4 position. Actually, the carbonyl group CO first underwent a 1e−, 1H+ reduction to form a neutral free radical, and the further 1e−, 1H+ reduction of the free radical was simultaneous with its following chemical reactions. When S2O2−8 was present, the free radical of vitamin P was oxidized by both S2O2−8 and its reduction intermediate, the sulfate radical anion SO•−4, to regenerate the original, which resulted in the production of a polarographic catalytic wave of vitamin P. Based on this catalytic wave, a novel method for the determination of vitamin P was proposed. In 0.02 M tartaric acid–sodium tartrate (pH 3.3) buffer containing 5.0 × 10−3 M K2S2O8, the peak potential of the catalytic wave was −1.42 V (vs SCE) and the peak current was rectilinear to the vitamin P concentration in the range of 8.0 × 10−9–1.0 × 10−6 M (r = 0.9994, n = 13). The catalytic wave of 2.0 × 10−7 M vitamin P enhanced the polarographic current 70 times compared with the corresponding reduction wave. The detection limit was 2.0 × 10−9 M, and the relative standard deviation at the 2.0 × 10−7 M level was 0.7% (n = 15). The proposed method was used for the determination of vitamin P content in the pharmaceutical preparation of tablets and the medicinal plant Sophora japonica L. without previous separation.