LAUSR

Abstract A method of ion-pair chromatography with direct conductivity detection was developed on a silica-based monolithic column for the fast and simultaneous determination of piperidinium and pyrrolidinium ionic liquid cations. The effects of the mobile phase, column temperature and flow rate on the retention of the cations were investigated. The retention rules were discussed. As an ion-pair reagent, sodium heptanesulfonate is more suitable than sodium pentanesulfonate for the separation and determination of piperidinium and pyrrolidinium cations. The increase of ion-pair reagent concentration led to the increased retention time of the cations. When acetonitrile content and mobile phase flow were increased, the retention time of the cations became shorter. The retention of piperidinium and pyrrolidinium cations is an exothermic process, and the retention of the cations conforms to the carbon number rule. The chromatographic analysis was performed using the Chromolith Speed ROD RP-18e column, 0.5 mmol/L sodium heptanesulfonate-5% acetonitrile as the mobile phase at a flow rate of 3.0 mL/min and column temperature of 30 °C. Separation of N -methyl- N -ethyl piperidinium, N -methyl- N -propyl piperidinium, N -methyl- N -butyl piperidinium and N -methyl- N -ethyl pyrrolidinium, N -methyl- N -propyl pyrrolidinium, N -methyl- N -butyl pyrrolidinium cations were achieved within 10 min. The detection limits (S/N = 3) were between 0.19 and 3.08 mg/L. Relative standard deviations ( n  = 5) for peak areas were less than 1.2%. The method has been applied to the determination of piperidinium and pyrrolidinium cations in ionic liquid samples. The spiked recoveries of ionic liquid cations were between 96% and 111%. The method is accurate, reliable, rapid, and has a better practicability.