Rapid analysis of melamine residue in milk, milk products, bakery goods and flour by ultra-performance liquid chromatography/tandem mass spectrometry: From food crisis to accreditation

A simple and rapid ultra-performance liquid chromatographic (UPLC) method with tandem mass spectrometry has been developed and validated for the determination of melamine in milk, milk products, bakery goods, and flour. The method comprises a simple extraction step with a solution of acetonitrile–water, ultrasound treatment and a liquid–liquid extraction with dichloromethane for fat removal. The purified extract is further diluted before injection on a ACQUITY BEH Hilic, with a total run of 2 min. Quantification of the results was performed with isotopic dilution (13C3-labelled melamine). No matrix effect was observed. Consequently solvent-based standards could be used for the calibration curve witch ranges from 0.5 mg/kg to 40 mg/kg. The calibration function was linear with a determination coefficient of >0.999 (r2). The limit of detection and the limit of quantification were respectively 0.2 and 0.5 mg/kg. Repeatability and within-lab reproducibility were <6% RSD. Average apparent recovery of melamine ranged from 97% to 99%. Accuracy of the method has been successfully tested by participating in two proficiency tests. The method is easily performed with confident quantification and provides a good alternative to solid phase extraction as well as to time-consuming derivatization prior to gas chromatography.