Abstract: The method for analyzing cyanuric acid in milk powder by gas chromatography tandem triple quadruple mass spectrometry (GC-MS/MS) with an isotopic internal standard and a multiple-reaction monitoring (MRM) system was established. The milk powder samples were extracted by methanol, and derivatized with BSTFA+TMCS (1%). The optimal parameters for instruments, matrix effects, fragment pathways of cyanuric acid derivatives and MRM scanning modes were explored. The ion peaks of cyanuric acid were m/z 345＞215 and m/z 345＞330 for qualitative and quantitative analysis, which was consistent with the ion peaks of isotopic internal standard with m/z 345＞215 and m/z 348＞217. The linear range of the developed method was between 0.010 mg/L and 0.50 mg/L and limit of detection was 0.014 mg/kg (RSN= 3). The relative standard deviations of the developed method varied between 3.4% and 4.8% and the average recovery rates of cyanuric acid from spiked samples between 90.0% and 102.5% in the range of 0.20 mg/kg to 2.0 mg/kg. The validation results and comparison with external standard method revealed that the developed method was accurate and reliable.

Key words: isotopic dilution mass spectrometry, multiple-reaction monitoring (MRM), derivation, cyanuric acid, milk powder