| A method was developed for the simultaneous determination of four pyridinium and five imidazolium ionic liquid cations by ion-pair chromatography coupled with ultraviolet detection.Chromatographic separations of the ionic liquid cations were performed on a reversed phase silica based column with ion-pair reagent water solution（pH adjusted with citric acid）+acetonitrile as mobile phase by gradient elution.Effects of ion-pair reagent type,acetonitrile concentration,column temperature and elution gradient on retention factor and separation of the ionic liquid cations were investigated.The retention rules of the ionic liquid cations on the column were discussed.The separation of the four pyridinium and five imidazolium ionic liquid cations were achieved using an optimized elution gradient of 1.0 mmol/L 1.heptanesulfonic acid sodium water solution（pH 4.0,A）+acetonitrile（B） with a flow rate of 1.0 mL/min at column temperature of 30 ℃.The optimized elution gradient was as follows: 0-3 min,12% B;3-3.5 min,12%-18% B;3.5-6.5 min,18% B;6.5-7.0 min,18%-25% B;7.0-10 min,25% B;10-10.5 min,25%-30% B;10.5-15 min,30% B.Under the optimal conditions,the four pyridinium and five imidazolium ionic liquid cations could be separated in 15 min.Detection limits（S/N=3） were in the range of 0.31-0.54 mg/L.Relative standard deviations（n=5） for the peak areas were 0.10%-0.75%.The method was successfully applied in the determination of the synthesized ionic liquid samples,with spiked recoveries of 94%-98% .The method is accurate,reliable and practical. |