Abstract: In order to improve the resolution and peak shape, 1-butyl-3-methylimidazolium tetrafluoroborate (［BMIM］BF4) was used as mobile phase additive to develop an HPLC method for the determination of four main alkaloids in Compound Kushen Injection. An Agilent TC-C18 column was used with the mobile phase of methanol-0.1% phosphoric acid solution (containing 2.2×10-4mol/L ［BMIM］BF4) (5:95, v/v), flow rate of 1.0 mL/min, column temperature of 30 ℃, and injection volume of 20 μL, detected at 205 nm. The calibration curves of matrine, sophoridine, oxymatrine and oxysophocarpine were in good linearity over the ranges of 25.8-155.0 mg/L, 40.0-240.0 mg/L, 21.7-130.0 mg/L and 37.5-225.0 mg/L, respectively, with correlation coefficients above 0.9990. The mean recoveries (n=9) were between 96.2% and 98.9%. Ionic liquid, ［BMIM］BF4, can obviously improve the resolution and peak shape. The method is simple, rapid, and reliable, and can be used for the determination of alkaloids in Sophora flavescens Ait in Compound Kushen Injection.

Key words: additive in mobile phase, alkaloids, Compound Kushen Injection, high performance liquid chromatography (HPLC), Sophora flavescens Ait, ionic liquid