Liquid chromatography-tandem mass spectrometry (LC-MS/MS) method extension to quantify simultaneously melamine and cyanuric acid in egg powder and soy protein in addition to milk products

As a consequence of the adulteration of infant formulas and milk powders with melamine (MEL) in China in 2008, much attention has been devoted to the analysis of MEL [and cyanuric acid (CA)] in dairy products. Several methods based on high-performance liquid chromatography (HPLC), liquid chromatography-tandem mass spectrometry (LC-MS/MS), nuclear magnetic resonance (NMR), or Raman spectroscopy have been described in the literature. However, no method is available for the simultaneous determination of MEL and CA in other raw materials, which are considered as high-risk materials for economically motivated adulteration. The present paper reports the results of an interlaboratory-based performance evaluation conducted with seven laboratories worldwide. The purpose was to demonstrate the ability of a cleanup-free LC-MS/MS method, originally developed for cow's milk and milk-powdered infant formula, to quantify MEL and CA in egg powder and soy protein. Limit of detection (LOD) and limit of quantification (LOQ) were 0.02 and 0.05 mg/kg for MEL in egg powder and soy protein, respectively. For CA, LOD and LOQ were 0.05 and 0.10 mg/kg in egg powder and 1.0 and 1.50 mg/kg in soy protein, respectively. Recoveries ranged within a 97-113% range for both MEL and CA in egg powder and soy protein. Reproducibility values (RSD(R)) from seven laboratories were within a 5.4-11.7% range for both analytes in the considered matrices. Horwitz ratio (HorRat) values between 0.4 and 0.7 indicate acceptable among-laboratory precision for the method described.