Liquid chromatography-tandem mass spectrometry multiresidue method for the analysis of quaternary ammonium compounds in cheese and milk products: Development and validation using the total error approach

- An efficient LC-MS/MS method was developed to quantify ten quaternary ammonium biocides.
- A single generic and fast extraction method of quaternary ammoniums in fat dairy products.
- The method was validated for cheeses and milk products.
- Total error concept was used for the validation of the developed methodology.
- Recovery values were almost all in the range 70-120%, RSD <20% and LOQs in the range 5-35 μg kg−1.

Quaternary ammonium compounds (QACs) are both cationic surfactants and biocidal substances widely used as disinfectants in the food industry. A sensitive and reliable method for the analysis of benzalkonium chlorides (BACs) and dialkyldimethylammonium chlorides (DDACs) has been developed that enables the simultaneous quantitative determination of ten quaternary ammonium residues in dairy products below the provisional maximum residue level (MRL), set at 0.1 mg kg−1. To the best of our knowledge, this method could be the one applicable to milk and to three major processed milk products selected, namely processed or hard pressed cheeses, and whole milk powder. The method comprises solvent extraction using a mixture of acetonitrile and ethyl acetate, without any further clean-up. Analyses were performed by liquid chromatography coupled with electrospray tandem mass spectrometry detection (LC-ESI-MS/MS) operating in positive mode. A C18 analytical column was used for chromatographic separation, with a mobile phase composed of acetonitrile and water both containing 0.3% formic acid; and methanol in the gradient mode. Five deuterated internal standards were added to obtain the most accurate quantification. Extraction recoveries were satisfactory and no matrix effects were observed. The method was validated using the total error approach in accordance with the NF V03-110 standard in order to characterize the trueness, repeatability, intermediate precision and analytical limits within the range of 5-150 μg kg−1 for all matrices. These performance criteria, calculated by e.noval® 3.0 software, were satisfactory and in full accordance with the proposed provisional MRL and with the recommendations in the European Union SANTE/11945/2015 regulatory guidelines. The limit of detection (LOD) was low (<1.9 μg kg−1) and the limit of quantification (LOQ) ranged from 5 μg kg−1 to 35 μg kg−1 for all matrices depending on the analytes.The validation results proved that the method is suitable for quantifying quaternary ammoniums in foodstuffs from dairy industries at residue levels, and could be used for biocide residues monitoring plans and to measure the exposition consumer to biocides products.