Synthesis of a Molecularly Imprinted Polymer for Melamine Analysis in Milk by HPLC with Diode Array Detection

Abstract

A molecularly imprinted polymer (MIP) for melamine was prepared by suspension polymerization, using melamine as a template, methacrylic acid as a functional monomer, and ethylene glycol dimethacrylate as a cross-linker. The optimal template/monomer and monomer/cross-linker ratios were obtained, being defined as 1/15 and 1/12, respectively. Molecular recognition properties and binding capacity toward melamine were evaluated by adsorption tests. Compared with the nonimprinted polymer, theimprinted polymer showed higher affinity for melamine with a dissociation constant (K-d) and a maximum binding concentration of 568.4 +/- 7.4 mol/L and 96.8 +/- 2.3 mol/g, respectively. Under optimal conditions, the imprinted polymer was used as a dispersive extraction sorbent to extract melamine from different milk samples, before high performance liquid chromatography with diode array detection (HPLC-DAD) analysis. The validated method presented a limit of detection of 0.6 mg/kg. From the analysis of six different milks, melamine was detected in two of the considered samples at a maximum concentration of 9.3 +/- 0.3 mg/kg.