Preparation of magnetic molecularly imprinted polymer for the extraction of melamine from milk followed by liquid chromatography-tandem mass spectrometry

In this work, a simple and selective method was successfully developed for the determination of melamine (MEL) in milk using magnetic molecularly imprinted polymer (MMIP) as sorbent. The MMIP has been prepared by using MEL as template molecule, methacrylic acid as functional monomer, ethylene glycol dimethacrylate as crosslinking agent and Fe3O4 magnetite as magnetic component. The extraction procedure was performed in a single step by blending and stirring the MMIPs and the milk sample which was diluted with water. The experimental results showed that the MMIP had high affinity and selectivity toward MEL. When the extraction was completed, the MMIPs absorbed MEL was separated from the sample matrix by an external magnet. The MEL eluted from the MMIPs was analysed by liquid chromatography-tandem mass spectrometry. For achieving optimal preconcentration and reducing non-specific interactions, various parameters affecting the extraction efficiency such as extraction solvent, the amount of MMIPs, extraction time, washing solution and eluting solution were evaluated. Under the optimal conditions, the linearity of quantification obtained by analyzing matrix-matched standards is in the range of 10-1000 ng mL−1. The detection limit of MEL is 2.6 ng mL−1. The relative standard deviations of intra- and inter-day ranging from 4.3% to 7.2% are obtained. The proposed method was successfully applied to determine MEL in five milk samples from different provenances. The recoveries of MEL are in the range of 88.0%-95.8%.