Collision-induced dissociation of corticosteroids in electrospray tandem mass spectrometry and development of a screening method by high performance liquid chromatography/tandem mass spectrometry

A screening method based on liquid chromatography/electrospray tandem mass spectrometry was developed in order to control the illegal use of corticost eroids as growth promoters in cattle. The objective was the detection of lo w residue levels of corticosteroids or metabolites in biological matrices. Relative to other studies published on this subject, the present work focus ed on enhancing specificity and sensitivity. Firstly, fragmentation of cort icosteroids by collision-induced dissociation was studied. In positive mode , the losses of H2O for each hydroxyl group fixed on the molecule, as well as the loss of HF or HCl for halogenated compounds, were observed. For high er collision energy, fragmentations in the B, C and D rings were induced, T he negative mode was found to be more specific, inducing a cleavage of the C-20-C-21 bond with concomitant loss of formaldehyde (CH2O), Secondly, thre e acquisition methods in the negative mode were studied and evaluated, reco rded signals being the parent ion [M + acetate](-) and the two daughter ion s, [M - H](-) and [M - H - CH2O](-). For dexamethasone, MS/MS instrumental detection limits of fragment ion and neutral loss scans, and of multiple re action monitoring (MRM), were 250, 20 and 5 pg injected, respectively, The MRM method was then evaluated with the objective of use for the detection o f corticosteroid residues in biological samples (urine, hair, muscle) and f or a metabolism study. Copyright (C) 2000 John Wiley & Sons, Ltd.