Methenamine in dairy products by isotope dilution gas chromatography coupled with triple quadrupole mass spectrometry: Method validation and occurrence

A gas chromatography coupled with triple quadrupole mass spectrometry (GC-MS/MS) method was developed for the determination of methenamine in dairy products. Methenamine-13C615N4 isotopic reference material was used as an internal standard to quantify the methenamine. The conditions of the extraction, solid phase extraction (SPE) and GC-MS/MS were optimized. Linear calibration curves were obtained over the calibration range of 1-100 μg/L (R2 = 0.9992). The limit of detection (LOD) was 2 μg/kg in the liquid sample and 8 μg/kg in the solid sample. The limit of quantification (LOQ) was 5 μg/kg in the liquid sample and 25 μg/kg in the solid sample. The average recovery of methenamine in dairy products varied from 93.3 to 102.3%. Method validation parameters, including precision and accuracy, were also evaluated. The intra-day precision ranged from 2.0 to 6.8%, with the accuracy varying from −6.7 to +2.3%. The inter-day precision ranged from 3.0 to 8.3%, with the accuracy varying from −8.5 to +1.6%. The method was applied to analyze forty-two dairy samples collected in Yunnan. The values of methenamine were observed from 11 to 18 μg/kg in milk samples, and 622-7310 μg/kg in cheese samples. Results of the stability test indicated that methenamine was more stable in milk powder than milk and cheese.