Analysis Of Morpholinium Ionic Liquid Cations By High Performance Liquid Chromatography With Indirect Ultraviolet Detection

An investigation into analysis of morpholinium ionic liquid cations withoutultraviolet absorption by high performance liquid chromatography was carried out. Thepurpose of this research is to develop simple, rapid and reliable methods to determineionic liquid cations by high performance liquid chromatography. This study mainlycontains three parts:Firstly, a fast analytical method was developed for the determination of N-methyl,propyl-morpholinium cation (MPMo) without ultraviolet (UV) absorption by ion-pairchromatography-indirect UV detection. Chromatographic separation was performed ona reversed-phase silica-based monolithic column using (background UV absorbingreagent ion-pair reagent) aqueous solution organic solvent as mobile phase. Theeffects of the background UV absorption reagents, detection wavelength, ion-pairreagents, organic solvents, column temperature and flow rate on the determination ofMPMo were investigated. The optimized chromatographic conditions for thedetermination of MPMo were as follows: using90%(v/v)(0.5mmol/L4-aminophenol hydrochloride0.1mmol/L1-heptanesulfonic sodium) aqueoussolution10%(v/v)methanol as mobile phase, and with the UV detectionwavelength of230nm, the column temperature of30oC, the flow rate of1.0mL/min.Under these conditions, the retention time of MPMo was2.966min. The detectionlimit (S/N=3) for MPMo was0.07mg/L. The relative standard deviations (n=5) forpeak area and the retention time were2.1%and0.02%, respectively. The method hasbeen successfully applied to the determination of morpholinium ionic liquidsynthesized by chemistry laboratory. Recovery of MPMo after spiking was98.8%. Themethod was simple, accurate and reliable.Secondly, a novel analytical method was developed for the determination ofmorpholinium ionic liquid cations without ultraviolet (UV) absorption by highperformance liquid chromatography-indirect ultraviolet detection using imidazoliumionic liquids as background UV absorption reagent. Chromatographic separation wasperformed on a reversed-phase C18column using imidazolium ionic liquid aqueoussolution organic solvent as mobile phase. The effects of the background UV absorption reagents, imidazolium ionic liquids and organic solvents on the separationand determination of morpholinium cations were investigated. The imidazolium ionicliquids in mobile phase were both the background UV absorption reagent of indirectUV detection and the active components to improve the separation of morpholiniumcations. The optimized chromatographic conditions for the determination ofmorpholinium cations were as follows:80%(v/v)0.5mmol/L1-ethyl-3-methyl-imidazolium tetrafluoroborate aqueous solution20%(v/v) methanolas mobile phase, UV detection wavelength was210nm, column temperature was30oC.Under these conditions, the baseline separation of N-methyl,ethyl-morpholiniumcations (MEMo) and MPMo was successfully achieved in8.5min. The detection limit(S/N=3) for MEMo and MPMo were0.15and0.29mg/L, respectively. Relativestandard deviations (n=5) for peak areas were1.19%and1.67%, respectively, andfor retention time were0.45%and0.69%, respectively. The method has beensuccessfully applied to the determination of two morpholinium ionic liquidssynthesized by chemistry laboratory. Recoveries of the cations after spiking were99.6%103.0%. It is a simple and practical method.Finally, a fast analytical method was developed for the determination of MPMowithout ultraviolet (UV) absorption by ion-pair chromatography-indirect UV detection.Chromatographic separation was performed on a reversed-phase silica-basedmonolithic column using (background UV absorbing reagent ion-pair reagent)aqueous solution organic solvent as mobile phase. The effects of the background UVabsorption reagents, detection wavelength, ion-pair reagents, organic solvents, columntemperature and flow rate on the determination of MPMo were investigated. Theoptimized chromatographic conditions for the determination of MPMo were as follows:85%(v/v)(0.5mmol/L1-ethyl-3-methyl-imidazolium0.1mmol/L1-heptanesulfonicacid sodium) aqueous solution15%(v/v)methanol as mobile phase, and with theUV detection wavelength of230nm, the column temperature of30oC, the flow rate of1.0mL/min. Under these conditions, retention time of MPMo was2.397min. Thedetection limit (S/N=3) for MPMo was0.02mg/L. The relative standard deviationsfor peak area and the retention time were1.08%and0.02%, respectively. The methodhas been successfully applied to the determination of morpholinium ionic liquidsynthesized by chemistry laboratory. Recovery of MPMo after spiking was100.5%.