Determination of Pyridinium Ionic Liquid Cations by Reversed Phase Ion-Pair Chromatography Using Gradient Elution

Four pyridinium ionic liquid cations (N-ethyl-pyridinium, N-butyl-pyridinium, N-butyl-4-methyl-pyridinium, N-hexyl-pyridinium) were separated and determined by reversed phase ion-pair chromatography with ultraviolet-visible detection. The effects of ion-pair reagent, acetonitrile concentration and column temperature on the retention and separation of the cations were evaluated. Then the four pyridinium cations could be separated at baseline within 13 min. The detection limits (S/N = 3) were 0.30–0.70 mg L^?1, and relative standard deviations (n = 5) for peak areas were 0.18–0.58%. The method was applied to analyze surface water with recoveries of 99.5–104.0%, which is accurate, reliable and practical.