Development of a simple method for simultaneous determination of nine subclasses of non-steroidal anti-inflammatory drugs in milk and dairy products by ultra-performance liquid chromatography with tandem mass spectrometry

A multi-residue analysis method for simultaneous determination of nine subclasses of non-steroidal anti-inflammatory drugs (NSAIDs) in milk and dairy products by ultra-performance liquid chromatography–tandem mass spectrometry (UPLC–MS/MS) has been established. The sample was initially extracted and deproteinized with ascorbic acid buffer (0.01 M, pH 3) and acetonitrile–ethyl acetate mixture, followed by centrifugation and evaporation, then reconstituted with acetonitrile-0.1% formic acid (1 + 1, v/v). After removal of lipid material by n-hexane, the sample was analyzed by UPLC–MS/MS with electro-spray ionization (ESI) interface in Multiple Reaction Monitoring (MRM) mode. The range of limits of detection (LODs) and limits of quantification (LOQs) were 0.03–0.30 μg/kg and 0.10–1.00 μg/kg, respectively. The recoveries in milk, milk powder, yogurt, processed cheese and milk beverage ranged from 61.7% to 117%, and the relative standard deviations (RSDs) were less than 17.9% at three spiked levels (1, 10 and 100 times of the LOQ). Matrix effects were also investigated and it was determined the signals of the analytes were suppressed from 9.4% to 76.6% in processed cheese. The proposed method was also applied to incurred sample analysis. The results proved that this method was suitable for the simultaneous determination of nine subclasses of NSAIDs residues in milk and dairy products.