Development of Isolation and Quantitation Methods for Dexamethasone in Human Plasma

摘要

An analytical method for the quantitation of nanogram to subnanogram levels of dexamethasone in human plasma utilizing GLC and chemical-ionization mass spectrometry is described. Dexamethasone in plasma was isolated, using a C18-bonded reversed phase cartridge and subsequent purification by normal phase HPLC. The purified dexamethasone was converted to its corresponding trimethylsilyl derivative and subjected to GLC-mass spectrometry. The quantitation by isotope-dilution mass spectrometry was carried out by selected ion monitoring on the (M+1)+ ions of the trimethylsilyl derivatives of dexamethasone and its stable isotopically labeled diluent, 13C6, 2H3-dexamethasone (681 and 690 m/z, respectively). Methane was used as the GLC carrier gas and as the chemical ionization reagent gas. The sensitivity of the method judged from the lower limit of detection of the mass spectrometer was at about 100 pg. The inter- and intra-assay coefficients of variation (C.V.) measured at two different concentrations were 3.83% and 3.78% for 2 ng/ml and 2.64% and 1.29% for 5 ng/ml, respectively.