Rapid confirmatory analysis of non-steroidal anti-inflammatory drugs in bovine milk by rapid resolution liquid chromatography tandem mass spectrometry

A rapid method has been developed to analyse carprofen (CPF), diclofenac (DCF), mefenamic acid (MFN), niflumic acid (NIFLU), naproxen (NAP), oxyphenylbutazone (OXYPHEN), phenylbutazone (PBZ) and suxibuzone (SUXI) residues in bovine milk. Milk samples are extracted with acetonitrile and sample extracts were purified on Evolute™ ABN solid phase extraction cartridges. Aliquots were analysed by rapid resolution liquid chromatography tandem mass spectrometry (RRLC-MS/MS) with a runtime of 6.5 min. The method was validated in bovine milk, according to the criteria defined in Commission Decision 2002/657/EC. CCα values of 0.46, 1.08, 0.92, 1.26, 1.29, 2.12, 0.55 and 2.86 ng mL^-1 were determined for CPF, DCF, MFN, NIFLU, NAP, OXYPHEN, PBZ and SUXI, respectively. CCβ values of 0.79, 1.85, 1.56, 2.15, 2.19, 3.62, 0.94 and 4.87 ng mL^-1 were determined for CPF, DCF, MFN, NIFLU, NAP, OXYPHEN, PBZ and SUXI, respectively. The measurement uncertainty of the method was estimated at 9, 28, 28, 45, 46, 45, 10 and 39% for CPF, DCF, MFN, NIFLU, NAP, OXYPHEN, PBZ and SUXI. Fortifying bovine milk samples (n = 18) in three separate assays, show the accuracy of the method to be between 82 and 108%. The precision of the method, expressed as RSD values for the within-lab reproducibility at the three levels of fortification (5, 7.5 and 10 ng mL^-1) was less than 16%, respectively. The advantage of the method is that low ng mL^-1 levels can be detected and quantitatively confirmed rapidly in milk and that 3 batches of samples can be analysed within a single day using RRLC-MS/MS with a runtime of 6.5 min.