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

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 H3PO4-KH2PO4 buffer solution because this buffer has a low conductivity signal which avoids interferences with cation detection. We obtained a detection limit of 0.003 mg/L for river samples. Precision and accuracy met the requirements of quantitative analysis.