Use of nano-liquid chromatography for the analysis of glycyrrhizin and glycyrrhetic acid in licorice roots and candies

Glycyrrhizin (G) and glycyrrhetic acid (GA) were separated by using nano-liquid chromatography (nano-LC) in a fused silica capillary packed with RP18 stationary phase (75 um ID, effective length 33 cm, packed 23 cm) eluting at 300 nL/min in a gradient mode. The mobile phase was a mixture of water-MeOH-MeCN-acetic acid (29:35:35: 1, v/v/v/v) that was delivered for one minute and after this was modified by reducing the water content (114:42.5:42.5: 1, v/v/v/v). The intra-day and inter-day relative standard deviations (of retention time and peak area) were satisfactory (lower than 2.9 and 4%, respectively). The linearity of the nano-LC method was assessed in the range 0.62-5.00 ug/mL and 80-200 ug/mL for GA and G, with R-2 = 0.996 and 0.995, respectively. The licorice was extracted with a mixture of ethanol-water, diluted with the mobile phase, and injected for the analysis.