Separation and Determination of Four Tanshinones in Danshen and Related Medicinal Plants by Micellar Electrokinetic Chromatography Using Ionic Liquids as Modifier

Abstract

A simple and fast micellar electrokinetic chromatography (MEKC) method using ionic liquids as modifier was established for simultaneous determination of four hydrophobic tanshinones, including dihydrotanshinone I (1), cryptotanshinone (2), tanshinone I (3) and tanshinone IIA (4), in Danshen and related medicinal plants. In normal MEKC using sodium dodecyl sulfate (SDS) as surfactant and organic solvents as additives, the four tanshinones, especially cryptotanshinone and tanshinone I, could not be well separated. Fortunately, further addition of ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim]BF4) resulted in a baseline separation of these four analytes. After an optimization study, 10 mM borax-10 mM SDS-10 mM [bmim]BF4 containing 15% acetonitrile (v/v) at pH 9.6 was adopted as the running buffer to complete the separation within 16 min at the voltage of 25 kV, temperature of 25°C and detection wavelength of 254 nm. The relative standard deviations of migration time and peak area were in the range of 0.62-2.21 and 1.33-3.90%, respectively, indicating the good repeatability of the developed method. This method was extensively validated by evaluating the linearity (R2 ≥ 0.9992), limits of detection (0.75-1.11 μg mL-1), limits of quantification (2.26-3.32 μg mL-1) and recovery (96.11-103.74%). Under the optimum conditions, samples of Danshen and related medicinal plants were well analyzed with high separation efficiency.