Quantitative determination of benzoic acid in liquid milk with liquid chromatography-tandem mass spectrometry

Objective:To establish a liquid chromatography-tandem mass spectrometric method(LC-MS/MS) for the determination of benzoic acid in commercial milk.Methods:Milk samples were deproteinized with methanol and benzoic acid concentration was determined by LC-MS/MS with negative electrospray ionization using deuterium-labelled internal standard(IS).Analyte and IS were detected on multiple reaction monitoring(MRM) mode by the transitions from the precursor to the product ion(m/z 121.0/77.0 and m/z 126.0/82.0).The retention time was 1.9 min and total run time was 5.0 min for each sample.Results:Calibration curve was linear in the range from 50 ng/ml to 5000 ng/ml with a correlation coefficient of 0.9997.The intra and inter-batch precision(RSD) ranged from 2.5%～3.9% and 3.6%～5.6%,and the recoveries were 102.6%～103.1% and 99.6%～102.2%.Among the liquid milk investigated,benzoic acid concentration of 112 ng/ml～5053 ng/ml was observed.Conclusion:The LC-MS/MS method is a simple,sensitive and specific assay for the quantitative determination of benzoic acid in milk.