Separation and on-line concentration of saponins from Panax notoginseng by micellar electrokinetic chromatography

A simple, reproducible and sensitive micellar electrokinetic chromatography (MEKC) method was developed for the separation and determination of 10 saponins from Panax notoginseng. Field-enhanced sample injection with reverse migrating micelles (FESI–RMM) was used for on-line concentration of the saponins. The effects of concentrations of sodium dodecyl sulfate (SDS) and organic modifier, the sample matrix, the injection time of water plug, the injection voltage and injection time of sample on the separation and stacking efficiency were investigated. The optimum buffer contained 10 mM H3PO4, 140 mM SDS, 20% acetonitrile and 15% 2-propanol and the pH of buffer was 2.4. The sample solution was diluted with 15 mM SDS and injected for 15 s with −8 kV after injection of 2 s water plug. Under the optimum conditions, the analytes were well separated with very high plate number (8.0 × 105–1.2 × 106 N/m); the limits of detection of the analytes were 1.7–6.3 μg/mL. The high sensitivity permitted the determination of two minor saponins Rh1 (1.01 mg/g) and Rg2 (0.62 mg/g) in P. notoginseng, which were not determined in the literature.