Quantitative determination of rhein in human plasma by liquid chromatography–negative electrospray ionization tandem mass/mass spectrometry and the application in a pharmacokinetic study

To investigate the pharmacokinetics of rhein in human, a liquid chromatography–electrospray ionization tandem mass/mass spectrometry (HPLC–ESI-MS/MS) method for the determination of rhein in human plasma is established in this study. Indomethacin is used as the internal standard (I.S.). The plasma samples are analyzed after protein precipitation with methanol, and the LC separation is performed on an Agilent Eclipse XDB-C18 column with a mobile phase of acetonitrile–0.2% formic acid water (70:30, v/v). The electrospray-ion source is performed in the negative mode. The multi-reaction monitoring mode is selected and the ion selected channels are set at m/z: 283.1 → 238.9 for rhein ([M−H]− → [M–CO2–H]−) and m/z: 356.2 → 312.0 for indomethacin ([M−H]− → [M–CO2–H]−), respectively. Calibration curve is linear over the range of 1.0–8000.0 ng/ml. The chromatographic separation is achieved within 12 min. The lower limits of quantification (LLOQ) is 1.0 ng/ml. The intra- and inter-run precisions are less than 4.65% and 8.28%, respectively. The method is successfully applied to determine the plasma concentrations of rhein in Chinese volunteers.