Study of the electrocatalytic effect of casein on the polarographic reduction of nickel(II). Determination of total proteins in milk by polarographic chronoamperometry

Abstract

Casein greatly reduces the overvoltage for the polarographic reduction of Ni^II in sodium acetate medium. Using polarographic chronoamperometry, current–time curves were obtained from which the electrocatalytic effect of casein could be evaluated. The variables affecting the electrochemical response were investigated and under selected experimental conditions [1 × 10^–2 mol l^–1 Ni^II, 1 mol l^–1 sodium acetate, pH = 7.0, T= 20 °C and E=–0.750 V (versus SCE)] casein was determined in the range 27–191 µg ml^–1. Application of the proposed method to the direct determination of total proteins in milk is demonstrated. The results obtained are consistent with those obtained with the established Kjeldahl method.