Reversed-phase ion-pair chromatography of hydroxyl functionalized imidazolium ionic liquid cations and its application in analysis of environmental water and measurement of hydrophobicity constants

A reversed-phase ion-pair chromatography with ultraviolet detection method for the determination of 1-hydroxyethyl-3-methyl imidazolium cation ([HOEtMIm](+)) and 1-hydroxypropyl-3-methyl imidazolium cation ([HOPrMIm](+)) was developed. The method has been applied to the analysis of hydroxyl functionalized imidazolium ionic liquid cations in Songhua River water samples and the determination of hydrophobicity constants. [HOEtMIm](+) and [HOPrMIm](+) were not completely separated in the reversed-phase chromatography, but complete separation was realized in the reversed-phase ion-pair chromatography. The effects of ion-pair reagents, organic solvents, column temperatures and ultraviolet detection wavelengths on the separation and detection of hydroxyl functionalized imidazolium ionic liquid cations in reversed-phase ion-pair chromato graphy were investigated. Ordinary imidazolium ionic liquids do not interfere with the determination of hydroxyl functionalized imidazolium ionic liquids. The suitable ion-pair reagent was sodium octane-sulfonate. Using reversed-phase C-18 chromatographic column, the mobile phase consisted of 0.5 mmol/L sodium octanesulfonate solution/methanol (85/15, v/v) with column temperature of 40 degrees C, ultraviolet detection wavelength of 210 nm and flow rate of 1.0 mL/min, [HOEtMIm](+) and [HOPrMIm](+) can be achieved baseline separation within 20 min. The detection limits were 0.36 and 0.50 mg/L, respectively. The relative standard deviations of peak area and retention time were less than 0.80%. Recoveries of sample addition were between 97.3% and 100.5%. The method was simple, accurate, reliable, satisfying the requirement of quantitative analysis, and has good practicability.