A novel analytical method was developed for the determination of alkyl sulfonates by high performance liquid chromatography-indirect ultraviolet detection using imidazolium ionic liquid as the background ultraviolet absorption reagent without ultraviolet absorption.Chromatographic separation was performed on a reversed-phase C18 column using imidazolium ionic liquid-organic solvent as mobile phase.Effects of detection wavelength,kinds and concentrations of organic solvents and imidazolium ionic liquids,and other parameters on the separation and determination of alkyl sulfonates were investigated.The retention rules of the alkyl sulfonates under different chromatographic conditions were discussed and the chromatographic conditions were optimized.The successful separation and detection of two alkyl sulfonates(sodium pentanesulfonate and sodium heptanesulfonate) were achieved using the optimized mobile phase of 0.7 mmol/L 1-ethyl-3-methyl-imidazolium tetrafluoroborate(pH 3.0,adjusted with 2 mmol/L monosodium phosphate-phosphoric acid)-methanol(55∶45) at a flow rate of 1.0 mL/min,a detection wavelength of 210 nm and a column temperature of 30 ℃.Under the optimal conditions, two alkyl sulfonates could be successfully separated in 10 min.The calibration curves showed good linearities in the ranges of 0.8-200 mg/L and 2.5-200 mg/L for two alkyl sulfonates,respectively,with correlation coefficients above 0.999.The detection limits of two alkyl sulfonates were 0.24 mg/L and 0.75 mg/L,respectively.The method was applied in the determination of environmental water samples,with spiked recoveries of 98.3%–99.1% and relative standard deviations less than 1.5%.The method was simple,accurate and reliable,and could meet the requirements for quantitative analysis.