Determination of Melamine by Diffuse Reflectance Spectroscopy by its Effect on the Formation of a Gold–Polyurethane Foam Nanocomposite

A chemical method is proposed for obtaining a nanocomposite based on gold nanoparticles (AuNP) and polyurethane foams (PUF). It includes the sorption of a reducing agent, sodium borohydride, on PUF from a solution containing sodium hydroxide as a stabilizer and cetyltrimethylammonium bromide as an ion-pair reagent, and the subsequent interaction of the modified polymer with chloroauric acid, leading to the formation of a colored nanocomposite. A possibility of using the process of the formation of a nanocomposite based on AuNP and PUF for the determination of melamine in milk powder and milk powder substitute by diffuse reflectance spectroscopy is evaluated. It is found that melamine affects the formation of this nanocomposite, causing a decrease in the intensity of the surface plasmon resonance band of gold nanoparticles in the material. It is proposed to use this effect for the determination of melamine by diffuse reflectance spectroscopy. The influence of the interaction time, the pH of the solution, and the concentration of chloroauric acid on the analytical signal, as well as the interfering effect of amino acids in the determination of melamine, are investigated. Under the chosen conditions, the limit of detection for melamine was 0.2 mg/L.