Determination of dexamethasone in human plasma and urine by electron-impact mass spectrometry

A gas chromatographic-electron-impact mass spectrometric method for the determination of dexamethasone in biological fluids has been developed. Quantitation by isotopedilution mass spectrometry was carried out by selected-ion monitoring on the molecular ions of the tetra(trimethylsilyl) derivative of dexamethasone and of dexamethasone M+9 (m/z 680 and 689, respectively). The sensitivity, specificity, precision and accuracy of the method were demonstrated to be satisfactory for application to pharmacokinetic and bioavailability studies of dexamethasone after administration of a therapeutic dose.