[Analysis of piperidinium ionic liquid cations by ion chromatography with direct conductivity detection]

A method of ion chromatography with direct conductivity detection was established to determine three piperidinium ionic liquid cations, i. e. N-methyl, ethyl piperidinium cation ([MEPi]+), N-methyl, propyl piperidinium cation ([MPPi]+) and N-methyl, butyl piperidinium cation ([MBPi]+). The effects of eluent types, eluent concentration and column temperature on the retention of the cations were investigated with sulfonic acid base cation exchange column using ethylenediamine-citric acid-acetonitrile as eluent. The results indicated that, with the increase of column temperature, the retention times of piperidinium cations were reduced, so the retention process of piperidinium cations was exothermic. The retentions of piperidinium cation homologue accorded with carbon number rule. The successful separation of the three piperidinium cations within 7 min was achieved using the optimized eluent of 0.2 mmol/L ethylenediamine-0.3 mmol/L citric acid-3% acetonitrile (pH 4.4) at a flow rate of 1.0 mL/min and the column temperature of 30 degrees C. Under these conditions, the detection limits at a signal-to-noise ratio of 3 for [MEPi]+, [MPPi] and [MBPi]+ were 0.14, 0.20 and 0.56 mg/L, respec-tively. The relative standard deviations (n = 5) for peak areas were less than 1.2%. The method has been applied to the determination of piperidinium ionic liquids synthesized in chemical laboratory with the spiked recoveries of 97.6% to 105.1%. The method is accurate, reliable, rapid, and has better practicability.