Simultaneous determination of 3‐n‐butylphthalide and its metabolite 10‐hydroxy‐butylphthalide in rat plasma using liquid chromatography–tandem mass spectrometry and application to a pharmacokinetic study

Abstract 3‐ n ‐Butylphthalide (NBP) is a potent drug for the treatment of ischemic stroke. The aim of this study was to develop a simple and sensitive ultra‐high‐performance liquid chromatography–tandem mass spectrometric (UPLC–MS/MS) method for the simultaneous determination of NBP and its circulating metabolite 10‐hydroxy‐NBP in rat plasma using senkyunolide I as the internal standard (IS). The analytes and IS were extracted from the plasma by ethyl acetate–ethyl ether (1:5, v/v ) and then separated on an ACQUITY BEH C 18 column (2.1 × 50 mm, 1.7 μm). The mobile phase consisted of water containing 0.1% formic acid and acetonitrile containing 0.1% formic acid, which was delivered at a flow rate of 0.3 mL/min with gradient elution. MS detection was achieved under selective reaction monitoring mode with precursor‐to‐product transitions at m/z 191.1 > 145.1 for NBP, m/z 207.1 > 171.1 for 10‐hydroxy‐NBP and m/z 207.1 > 161.1 for IS, respectively. The assay showed excellent linearity over the concentration range of 0.5–1000 ng/mL for both analytes, with correlation coefficient greater than 0.998. The other validation parameters were all within the required limits. The validated UPLC–MS/MS method has been further applied to the pharmacokinetic study of NBP and 10‐hydroxy‐NBP in rats after they were orally administered with NBP (30 mg/kg).