Ion Exchange Chromatography-Indirect Ultraviolet Detection for Separation and Determination of Morpholinium Ionic Liquid Cations

A rapid analytical method of ion exchange chromatography with indirect ultraviolet detection was developed to determine morpholinium ionic liquid (IL) cations, i.e. N-methyl-N-ethyl morpholinium cation ([MEMo]⁺) and N-methyl-N-propyl morpholinium cation ([MPMo]⁺). Chromatographic separation of morpholinium cations was performed on a sulfonic acid base cation exchange column using imidazolium ionic liquid-organic solvent as mobile phase. The effects of chromatographic columns, ultraviolet absorption reagents, imidazolium ILs, detection wavelength, organic solvents, pH values of the mobile phase and column temperature on the retention of morpholinium cations were investigated. The retention times of the cations were clearly decreased by the increase of the alkyl substituent length on imidazolium cation or with the increase of the concentration of 1-ethyl-3-methyl imidazolium tetrafluoroborate. The molecular structure of the anion of imidazolium IL which has UV absorption has influence on determination of the analytes. Under the optimal conditions, the detection limits (signal-to-noise ratio, S/N = 3) were 0.29 and 0.44 mg L^-1 The method has been successfully applied to the determination of two ILs synthesized by chemistry laboratory. The method uses the liquid chromatography system, which is widely available in general laboratories, and the simple composition of mobile phase, thus make the quantitative analysis of no UV absorption morpholinium cations possible.