Determination of Matrine and Oxymatrine in Sophora Flavescens by Nonaqueous Capillary Electrophoresis-Electrospray Ionization-Ion Trap-Mass Spectrometry

A simple, rapid, and sensitive nonaqueous capillary electrophoresis-electrospray ionization-ion trap-mass spectrometry (NACE-ESI-IT-MS) method was developed for determination of matrine and oxymatrine in Sophora Flavescens and medicinal preparations. The conditions for NACE separation and MS detection were systematically optimized. The optimum NACE buffer contained 30 mM ammonium acetate, 1% acetic acid, and 15% acetonitrile in methanol and the applied voltage on separation capillary was set at 25 kV. Berberine was selected as internal standard. In order to generate a stable electrospray, a sheath liquid (isopropanol/H2O, 2/1, v/v) was used, which could also boost the flow through the ESI needle. The matrine and oxymatrine solutions were introduced into MS detection by a syringe pump for collecting the MSn spectra to investigate the main fragment ions and its possible cleavage pathways. Both matrine and oxymatrine showed good linearity in the concentration ranges from 0.5 to 400 µg/mL, with linear correlation coefficient R > 0.99 and the limit of detections were 37.5 ng/mL for matrine and 50.0 ng/mL for oxymatrine, respectively. The recoveries at different content of Sophora Flavescens were 98.3%–102.9% for MT and 95.3%–100.6% for OMT, which indicates the reliability of this method.