A simple and reliable liquid chromatography-tandem mass spectrometry method for determination of ochratoxin A in hard cheese

This paper reports a simple and reliable mass spectrometry hyphenated chromatographic method for ochratoxin A determination in hard cheese. The method is based on a simple extraction using an acetonitrile:water (84:16, v/v) solution acidified with 2.5% acetic acid. After a defatting step with n-hexane, the extract was directly analysed by LC-MS/MS without any further clean-up step. The method showed good linearity and specificity, and it was in-house validated in the range of 1-16 μg/kg, resulting in 93.75% mean overall recovery (confidence interval 1.36%) and 3.42% coefficient of variatioin (CV). The analytical performances were also satisfactory in terms of sensitivity (limit of quantification = 1 μg/kg); although no legal limits have been set up for cheese, this value is consistent with the tolerances fixed for other regulated foods. Preliminary results on 40 commercial samples of grated hard cheese are presented.