Determination of melamine and cyromazine in milk by high performance liquid chromatography coupled with online solid-phase extraction using a novel cation-exchange restricted access material synthesized by surface initiated atom transfer radical polymerization.

A novel strong-cation-exchange restricted access material has been synthesized by atom transfer radical polymerization (ATRP). In the synthesis, poly(3-sulfopropyl methacrylate-co-ethylene dimethacrylate), [p(SPM/EDMA)] was grafted on the silica by surface-initiated ATRP first. The poly(glycerol mono-methacrylate) [pGMMA] was then immobilized on the external surface, which created a chemical diffusion barrier for protein exclusion. The resulting Sil-g-p(SPM/EDMA)-g-pGMMA has both functions of protein exclusion and cation exchange, exhibiting the property of cation-exchange restricted access material. The application of Sil-g-p(SPM/EDMA)-g-pGMMA has been studied by the determination of melamine and cyromazine in bovine milk using the online solid-phase extraction/HPLC method. In the process, the Sil-g-p(SPM/EDMA)-g-pGMMA was used for the sample pre-treatment and a HILIC column was employed as the analytical column. The method has shown good accuracy, precision and low limits of detections. The result demonstrated that the Sil-g-p(SPM/EDMA)-g-pGMMA can be used for the cation extraction from biological samples by direct HPLC injection.