A highly sensitive ultra performance liquid chromatography–tandem mass spectrometric (UPLC–MS/MS) technique for quantitation of protein free and bound efavirenz (EFV) in human seminal and blood plasma

A combined UPLC–tandem mass spectrometric (UPLC–MS/MS) technique has been validated for quantitation of protein free efavirenz (EFV) as well as total concentrations of EFV in human blood and seminal plasma. The analytical method possesses capabilities for concentration measurements of EFV ranging from 0.5 to 10,000 ng/ml with an accuracy (%dev) of −5.2–8.0% and precision (%CV) of <8%. Standard curves were linear with coefficients of variation (r2) >0.98. The method employs a racemic fluorinated analog of EFV (F-EFV) as the internal standard. EFV and F-EFV were eluted from a reverse-phase UPLC column via gradient elution with detection via negative ion multiple reaction monitoring (MRM). EFV and F-EFV, respectively, were detected via the following MRM transitions: m/z 314.0 > 244.1 and m/z 298.0 > 227.9. The time required for the analysis of each sample was 8.0 min. The analytical technique is capable of a reliable detection limit of ∼15–20 fmol of EFV injected on column.