Separation of Fluoroquinolones by MEKC Modified with Hydrophobic Ionic Liquid as a Modifier

The hydrophobic ionic liquid [BMIM]PF₆ (1-butyl-3-methylimidazolium hexafluorophosphate) can interact with sodium dodecyl sulfate (SDS) micelles in aqueous solution and modify their physicochemical properties to produce a unique separation efficiency in micellar electrokinetic chromatography (MEKC). An MEKC method was developed using [BMIM]PF₆ as a modifier for separating eight fluoroquinolone compounds (ciprofloxacin, enrofloxacin, gatifloxacin, ofloxacin, norfloxacin, enoxacin, pazufloxacin, and tosufloxacin). The effects of several parameters on the separation selectivity, e.g., pH, concentration of background electrolyte, concentration ratio and amount of [BMIM]PF₆ and SDS, were investigated. Under the optimal conditions of 10 mmol L⁻¹ sodium borate, pH 7.1, 1.7% (w/w) SDS, 1.5% (w/w) [BMIM]PF₆ with 18 kV as running voltage, the eight investigated quinolone compounds were baseline separated within 15 min. The selectivity of the developed method differed from that of the simple SDS micelles system containing no ionic liquid. The results suggest that hydrophobic ionic liquids should be promising modifiers in capillary electrophoresis, especially in MEKC analysis.