A Prospective and Cost-Effective Voltammetric-Chemometric Approach for the Discrimination and Quantification of Melamine and Urea in Milk

In this work, an analytical approach combining voltammetric detection with chemometric analysis was developed to discriminate melamine and urea adulterants in milk products. The electrochemical measurement was performed using a glassy carbon electrode (GCE) modified with acid-functionalized multiwalled carbon nanotubes (f-MWCNTs), which served as the working electrode to obtain the voltammetric fingerprint. This electrode was used to measure the voltammetric response of fresh cow milk adulterated with melamine and urea in 0.1 M KCl as the electrolyte by employing cyclic voltammetry (CV). Based on this result, milk adulterated with melamine and urea displayed broad peaks in the potential range of 0.6-0.8 V versus Ag/AgCl, attributable to the electroactive components in the adulterants and the milk. Additionally, it was found that milk adulterated with melamine exhibited several reduction peaks in the potential range from -0.4 to 0 V versus Ag/AgCl, corresponding to the reduction reaction of components present in melamine. Further chemometric analysis, i.e., principal component analysis, effectively distinguishes cow milk adulterated with melamine and urea. Moreover, the discrimination between cow's milk and its adulterants was successfully achieved using hierarchical cluster analysis, with the lowest melamine concentration detected at 0.24%. Quantitative estimates of milk adulterants were predicted using partial least-squares regression, as determined by root-mean-square error cross-validation (RMSECV), with melamine at 0.0755% and urea at 0.0064%. Therefore, this result demonstrates a promising, cost-effective analytical technique that can be further developed into a novel approach for detecting adulterants in dairy products for practical applications.