Extraction and detection of quaternary ammonium ionic liquid cations in water samples

Abstract

The recent development of ionic liquids may induce environmental pollution, yet there is a lack of sensitive analytical methods to detect traces of ionic liquids, notably for quaternary ammonium ionic liquids. Here, we set up a method based on solid-phase extraction and ion chromatography combined to analyze quaternary ammonium ionic liquid cations in river water samples. Cations included tetramethylammonium, tetraethylammonium, tetrapropylammonium and tetrabutylammonium. We used methanesulfonic acid–acetonitrile as mobile phase in a cation-exchange column with carboxylic acid functional groups. A strong acid cation-exchange solid-phase extraction column was used for extraction and enrichment, then water–methanol was eluted to wash impurities, and finally the analytes were eluted with H 3 PO 4 –KH 2 PO 4 buffer solution because this buffer has a low conductivity signal which avoids interferences with cation detection. We obtained a detection limit of 0.003\xa0mg/L for river samples. Precision and accuracy met the requirements of quantitative analysis.