Residue analysis of glucocorticoids in bovine milk by liquid chromatography–tandem mass spectrometry.

Caretti, Fulvia; Gentili, Alessandra; Ambrosi, Annalisa; Rocca, Lucia Mainero; Delfini, Maurizio; Cocco, Maria Enrica Di; D'Ascenzo, Giuseppe

A sensitive liquid chromatography–tandem mass spectrometry (LC-MS/MS) method for the simultaneous determination of 13 steroidal anti-inflammatory drugs in bovine milk is presented. Due to their weakly acid nature, analytes were separated by ion suppression reversed phase chromatography and detected in positive-ion mode by a high flow electrospray source. Dexamethasone-d4 was used as internal standard. The sample preparation was simple and reliable; it included acidic deproteinization of milk followed by sample enrichment and clean-up, utilizing a C18 solid phase extraction cartridge. Recoveries exceeded 70% with an intra-day precision not larger than 12%. The efficiency of the sample clean-up and internal standardization rendered negligible the matrix effect, estimated by comparing standard and matrix-matched calibration curves. A small-scale reconnaissance was carried out on several raw and whole fresh milk samples. A large number of analyzed samples showed a chromatographic peak, in the retention time window of cortisol, at levels included between its decision limit (CCα) and detection capability (CCβ). As a result of a heat-induced transformation, an isomeric product of triamcinolone was observed during the extract evaporation. Since this rearrangement might occur during the milk pasteurization process, LC-MS/MS and 1H-NMR investigations were performed out to conclusively differentiate the two isomers. One- and two-dimensional proton NMR spectra were able to identify the transformation product as 9a-fluoro-11b,16a-trihydroxy-17b-hydroxymethyl- D-homoandrosta-1,4-diene-3,17a-dione.

LIQUID chromatography; MASS spectrometry; GLUCOCORTICOIDS; COWS; MILK; ELECTROSPRAY ionization mass spectrometry; TRIAMCINOLONE; MATRIX effect

Analytical & Bioanalytical Chemistry, 2010, Vol 397, Issue 6, p2477

1618-2642

Academic Journal

10.1007/s00216-010-3774-9