In this study, an analytical method of hydrophilic interaction liquid chromatography combined with indirect ultraviolet detection for the determination of alkyl ammonium ionic liquid cations was developed, and it was combined with the sample pretreatment technique of solid phase extraction in order to be applied to analysis of alkyl ammonium ionic liquid cations in environmental water. The retention behavior of alkyl ammonium cations on the hydrophilic interaction column had the typical characteristics of hydrophilic interaction liquid chromatography, and their retention followed the carbon number rule. The separation and detection of tetraethyl ammonium cations, tetrapropyl ammonium cations and tetrabutyl ammonium cations were achieved in 20 min by using 1.0 mM 1-ethyl-3-methyl imidazolium trifluoroacetate aqueous solution/acetonitrile (40/60, v/v) as the mobile phase. The detection limits were 0.093, 0.096 and 0.253 mg L−1, respectively. The relative standard deviations of the retention time and the peak area were less than 0.5% from seven determinations. The reversed phase ion-pair solid phase extraction method was realized by using sodium octanesulfonate as the ion-pair reagent and 90% acetonitrile (v/v) solution as the eluent. Alkyl ammonium cations in Songhua River water and Hulan River water were analyzed. The results showed that the recoveries and enrichment effect of tetraethyl ammonium cations and tetrapropyl ammonium cations were all good. The method is simple and reliable, which can provide a reference for the analysis of alkyl ammonium cations in environmental water.
