Quantification of epimeric budesonide and fluticasone propionate in human plasma by liquid chromatography-atmospheric pressure chemical ionization tandem mass spectrometry

A highly sensitive and selective liquid chromatography-atmospheric pressure chemical ionization tandem mass spectrometry assay was developed and valid ated for simultaneous determination of epimeric budesonide (BUD) and flutic asone propionate (FP) in plasma. The drugs were isolated from human plasma using C-18 solid-phase extraction cartridges, and epimeric BUD was acetylat ed with a mixture of 12.5% acetic anhydride and 12.5% triethylamine in acet onitrile, to form the 21-acetyl derivatives following the solid-phase extra ction. Deuterium-labelled BUD acetate with an isotopic purity > 99% was syn thesized and used as the internal standard. The assay was linear over the r anges 0.05-10.0 ng/ml for epimeric BUD, and 0.02-4.0 ng/ml. for FP. The int er- and intra-day relative standard deviations were < 14.3% in the assay co ncentration range. (C) 2001 Elsevier Science B.V. All rights reserved.