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

• NACE of flavonoids (quercetin, luteolin, kaempferol) in ACN using three different ionic liquids.
• Selection of ionic liquid type and concentration influences migration and alters selectivity.
• High concentrations of ionic liquid can be used in combination with MeOH to improve solubility of the flavonoids.
• The NACE IL method is suitable for the detection of flavonoids in Semen Plantaginis.

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.