Imidazolium ionic liquid as the background ultraviolet absorption reagent for determination of morpholinium cations by high performance liquid chromatography-indirect ultraviolet detection

A novel analytical method was developed for determining morpholinium cations lacking ultraviolet absorption groups. This determination was carried out by high performance liquid chromatography-indirect ultraviolet (HPLC-IUV) detection using imidazolium ionic liquid as background absorption reagents, and imidazolium ionic liquid aq. soln.-organic solvent as mobile phase by a reversed-phase C18 column. The background ultraviolet absorption reagents, imidazolium ionic liquids and organic solvents were investigated. The imidazolium ionic liquid in the mobile phase is not only the background ultraviolet absorption reagent for IUV, but also an active component to improve the separation of morpholinium cations. It was found that morpholinium cations could be adequately determined when 0.5 mmol/L 1-ethyl-3-methylimidazolium tetrafluoroborate aq. soln./methanol (80:20, v/v) was used as mobile phase with an IUV detection wavelength of 210 nm. In this study, the baseline separation of Nmethyl, ethylmorpholinium cations (MEMo) and N-methyl, propylmorpholinium cations (MPMo) was successfully achieved in 8.5 min. The detection limits (S/N = 3) for MEMo and MPMo were 0.15 and 0.29 mg/L, respectively. This simple and practical method has been successfully applied to the determination of two morpholinium ionic liquids synthesized by the chemistry laboratory.