Analysis of flavonoids by non-aqueous capillary electrophoresis with 1-ethyl-3-methylimidazolium ionic-liquids as background electrolytes

The separation of three flavonoids, kaempferol, quercetin and luteolin, by capillary zone electrophoresis with three 1-ethyl-3-methylimidazolium ionic liquids (ILs), namely chloride, hydrogen sulfate and tetrafluoroborate salts, under non-aqueous conditions using acetonitrile as solvent was investigated. Depending on the IL, the three flavonoids can be separated under positive voltage with a low IL concentration and negative voltage with a high IL concentration. The separations are based on heteroconjungation between the IL anions and the analytes. The heteroconjungation between the anions of the ILs and the analytes is proton sensitive and only a very small amount of protic solvents, such as methanol, added into the electrolyte solution can harm the separation, but higher IL concentrations can overcome this higher amount of protic solvents. Using a high concentration of IL in the sample was used to enhance the flavonoid solubility by as much as 10, overcoming the problem of the low solubility during NACE analysis with ACN as the solvent. Finally, kaempferol, quercetin and luteolin in Semen Plantaginis were analysed by nonaqueous capillary electrophoresis with low concentration of the hydrogen sulfate ionic liquid with excellent results.