A liquid chromatography-electrospray tandem mass spectrometry method was developed and validated to quantitate celecoxib in human plasma. The assay was based on protein precipitation with methanol and liquid chromatography on a C₁₈ column (55 mm × 2 mm, 3 μm), the mobile phase consisted of methanol-10 mM ammonium acetate (75:25, v/v). Quantification was performed by mass spectrometry in the multiple reaction monitoring mode with negative electrospray ionization at m/z 380→316 and 384→320 for celecoxib and the internal standard celecoxib-D₄, respectively. The lower limit of quantitation was 7.0 ng/ml using 0.1 ml of plasma and linearity was demonstrated up to 1800 ng/ml. Intra-assay and inter-assay precision expressed by relative standard deviation was less than 4% and inaccuracy did not exceed 6% at all levels. The assay was applied to the analysis of samples from a pharmacokinetic study.
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