Determination of a cyclooxygenase II inhibitor in human plasma by capillary gas chromatography with mass spectrometric detection

Sensitive methods based on capillary gas chromatography (GC) with mass spectrometric (MS) detection in a selected-ion monitoring mode (SIM) for the determination of a cyclooxygenase II (COX-II) inhibitor (3-isopropoxy-4-(4-methanesulfonylphenyl)-5,5′-dimethyl-5H-furan-2-one, I) in human plasma, in two concentration ranges of 0.1–20 and 5–1000 ng/ml, are described. Following liquid–liquid extraction, the residue, after evaporation of the organic phase to dryness, was reconstituted in acetonitrile (20 μl) and part of the extract (1 μl) was analyzed by GC/MS/SIM. The drug (I) and internal standard (II) were separated on a 25 m×0.2 mm capillary column with HP Ultra 1 (100% dimethylpolysiloxane, 0.33 μm) phase and analyzed by MS/SIM monitoring ions at m/z 237 and 282 for I and II, respectively. The standard curve was linear within the lower concentration range of 0.1–20 ng/ml and the lower limit of quantification (LLOQ) in plasma was 0.1 ng/ml. Intraday coefficients of variation (CV, n=5) were 8.9, 4.2, 5.7, 3.1, 1.9, 1.9, and 4.4% at 0.1, 0.2, 0.5, 1.0, 5.0, 10, and 20 ng/ml, respectively. The standard curve was also linear within the higher concentration range of 5–1000 ng/ml and the LLOQ in plasma was 5 ng/ml. Intraday coefficients of variation (CV, n=5) were all below 9% at all concentrations within the standard curve range. The accuracy for I in human plasma was 91–112% and the recovery of I and II was greater than 70% at all concentrations within both standard curve ranges. The details of the assay methodology are presented.