On-line concentration by field-enhanced sample injection with reverse migrating micelles in micellar electrokinetic capillary chromatography for the analysis of triterpenoids from traditional chinese medicine

In this work, a simple, reproducible and sensitive micellar electrokinetic chromatography (MEKC) method was developed for the separation and determination of five triterpenoids, lupeol (1), 1 beta-hydroxy-lupeol (2), lup-3 beta,1 alpha-diol (3), lup-1 beta,3 beta,11 alpha-triol (4) and 30-norlupan-3 beta,11 alpha-diol-20-one (5) in traditional Chinese medicine of Salvia roborowskii Maxim. Field-enhanced sample injection with reverse migrating micelles (FESI-RMM) was used for on-line concentration of triterpenoids. The optimum buffer contained 50 mM H(3)PO(4), 160 mM SDS, 20% acetonitrile and 15% 2-propanol and pH of buffer was 2.0. The sample solution was diluted with 10 mM H(3)PO(4) (pH 2.5, containing 10 mM SDS) and injected for 15 s with -8 kV after injection of 4 s water plug. 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. Under the optimum conditions, the analytes were well separated and by optimizing the stacking conditions, about 28-96-fold improvement in the detection sensitivity was obtained for triterpenoids. The contents of five triterpenoids in Salvia roborowskii Maxim were successfully determined with satisfactory repeatability and recovery.