Simultaneous determination of betamethasone and dexamethasone residues in bovine liver by liquid chromatography/tandem mass spectrometry

In this study a new method for the simultaneous confirmation of betamethaso ne and dexamethasone residues in bovine liver is presented. A Quattro LCZ t riple quadrupole mass spectrometer, equipped with an atmospheric pressure i onization (API) source, was coupled to a high performance liquid chromatogr aph (HPLC) system. Spiked liver samples were first extracted with acetonitr ile, and the extracts were purified on C-18 columns. LC separations were pe rformed on a Hypercarb column, with acetonitrile/water (90:10, v/v, +0.3% f ormic acid) as the mobile phase. Retention times for dexa-and betamethasone were 6.60 and 8.50 min, respectively. Fluorometholone had a retention time of 6.70 min and was used as the internal standard. The detection of the an alytes was performed in the multiple reaction monitoring (MRM) mode. The as say was linear over the range of 0.5 to 8 mug/kg for both analytes. The est imated determination limits were 0.2 mug/kg for both beta- and dexamethason e and the quantification limits were 0.4 mug/kg for dexamethasone and 0.3 m ug/kg for betamethasone. Analysis precision at 1, 2 and 4 mug/kg was lower than 6.1% (relative standard deviation, RSD) and accuracy was at least 97.5 %. Recoveries at 1, 2 and 4 mug/kg ranged between 56 and 69%. Copyright (C) 2001 John Wiley & Sons, Ltd.