Rapid multi-residue method for the quantitative determination and confirmation of glucocorticosteroids in bovine milk using liquid chromatography–electrospray ionization–tandem mass spectrometry

Dexamethasone, betamethasone and prednisolone are synthetic glucocorticosteroids authorised for therapeutic use in bovine animals within the European Union. Dexamethasone and betamethasone are used mainly for the treatment of metabolic and inflammatory diseases. Prednisolone is used to treat bovine mastitis. Maximum residue limits (MRLs) of 0.3 μg kg−1 for both dexamethasone and betamethasone and 6.0 μg kg−1 for prednisolone in bovine milk have been established. 6α-Methylprednisolone and flumethasone are not authorised for use in bovine animals and are completely banned in bovine milk. The proposed method is based on deprotenisation of milk using 20% (w/v) trichloroacetic acid. Samples are filtered using glass microfibre filters and subject to clean-up using OASIS HLB solid phase extraction. Separation was achieved on a Hypercarb 100 mm × 2.1 mm × 5 μm column. Mobile phase was: 90/10 acetonitrile/0.1% formic acid in water; flow rate was 600 μL min−1. The method allowed the rapid identification and confirmation of the five glucocorticosteroids according to the criteria laid down in Commission Decision 2002/657/EC. Matrix calibration curves for all compounds were linear in the interval 0.0 MRL to 2.0 MRL with a correlation coefficient (r2) higher than 0.96. Relative recoveries ranged from 97% for betamethasone to 111% for prednisolone. Precision at the MRL ranged from 3.8% for prednisolone to 13.8% for betamethasone. Decision limits, CCα, and detection capability, CCβ have been calculated for all compounds.