Use of copper electrode for melamine quantification in milk

We report the development of a simple analytical method that offers reagentless sensing capabilities by using a copper sensor for monitoring melamine. In this method, the anodic dissolution of the copper electrode is initiated electrochemically to release copper ions, which form the melamine chloride copper ionic pair at the electrode surface. After this process, the melamine chloride copper ionic pair can be reduced electrochemically at the surface of the electrode and quantified under the optimized conditions. This protocol eliminates the necessity to contaminate the sample with a copper salt, making the method proposed herein more environmentally benign than other techniques. The elucidation of the electrochemical reduction process of the melamine copper ionic pair was investigated with an electrochemical quartz crystal microbalance (EQCM). The quantification of melamine in milk was performed using differential pulse voltammetry, where the peak current response was found to increase linearly with melamine concentration over the range 5-90 mu mol L-1. The repeatability of the electrode response was evaluated as 1% (n = 20), and the detection limit of the proposed method was estimated to be 0.85 mu mol L-1 (3s/slope). The accuracy of the proposed method was evaluated using milk samples and an addition and recovery protocol.