Chemical Separation of Bioactive Licorice Compounds Using Capillary Electrophoresis

Abstract

Four bioactive components derived from licorice root, i.e., glycyrrhizin (GL), 18α‐glycyrrhetinic acid (18α‐GA), 18β‐glycyrrhetinic acid (18β‐GA), and isoliquiritigenin (IQ) were separated by capillary electrophoresis (CE). For the first time, separation of diastereoisomers of 18α‐GA and 18β‐GA by CE using a chiral additive has been achieved. Simultaneous separation of the above four pharmacological active components in one run by CE was reported. Different modes of CE, such as capillary zone electrophoresis (CZE), micellar electrokinetic capillary chromatography (MECC), cyclodextrin‐MECC (CD‐MECC), were employed to optimize the chemical separation. Preliminary experiments started with CZE using a 50 mM sodium tetraborate buffer within a capillary tube of inner diameter 50 µm and length of 60.2 cm. A CE separation voltage of 17 kV was used. Detection was achieved at a distance of 50 cm from the capillary inlet using a diode array UV absorbance detector over the wavelength range from 190 to 300 nm. The optimum separation was achieved by 10 mM sodium tetraborate‐15 mM β‐CD‐25 mM SC. The effects of various experimental parameters, including pH, surfactant concentration, temperature, and organic modifier, on effective separation were investigated. The conditions of pH 8.5 and temperature at 25°C have resulted in more effective separations.