Determination of alprostadil in rat plasma by ultra performance liquid chromatography-electrospray ionization-tandem mass spectrometry after intravenous administration

A rapid, highly selective ultra performance liquid chromatography-electrospray ionisation-tandem mass spectrometry method (UPLC-ESI-MS/MS) was developed and validated for the determination and pharmacokinetic investigation of alprostadil in rat plasma. After a simple sample preparation procedure involving a one-step liquid-liquid extraction, alprostadil and the internal standard, diphenhydramine, were chromatographed on an ACQUITY UPLC™ BEH C18 column with gradient elution using a mobile phase consisting of acetonitrile and water (containing 0.1% formic acid) at a flow rate of 0.25 mL min−1. The detection was performed on a triple quadrupole tandem mass spectrometer in multiple reaction monitoring (MRM) mode via an electrospray ionization (ESI) source. The calibration curve was linear (r2 = 0.99) over the concentration range 0.4-250.0 ng mL−1, with a lower limit of quantification of 0.4 ng mL−1 for alprostadil. The inter- and intra-day precision (%R.S.D.) was less than 8.5% and 2.4%, respectively, and the accuracy (RE%) was between 9.3% and 1.0% (n = 6). Alprostadil in rat plasma was stable when stored at room temperature for 0.5 h and at −20 °C for two weeks. The method was very rapid, simple and reliable, and was employed for the first time for the pharmacokinetic studies of alprostadil in rats after a single intravenous administration of 50 μg kg−1.