Quantitative analysis of RU38486 (mifepristone) by HPLC triple quadrupole mass spectrometry

A sensitive liquid chromatography–mass spectrometric method was validated for the quantification of RU38486 (mifepristone) in human and murine plasma. The analyte and internal standard (alfaxolone) were extracted by liquid–liquid extraction with diethyl ether, resolved on a C18 column using gradient elution with methanol and ammonium acetate and detected after positive electrospray ionization (m/z 430 → 372; m/z 333 → 297, respectively). Quantification was linear over the range 0.5–500 ng (r2 > 0.997), precise and accurate (intra-assay RSD ≤ 7.2%, RME ≤ 8.2%; inter-assay RSD ≤ 15.7% RME ≤ 10.2%). The limit of quantification (LOQ) was 50 pg injected on column, permitting reproducible analysis of RU38486 in small volumes of plasma.