Ion chromatography for monitoring [NTf2]− anion contaminants in pure and saline water

Abstract

Hydrophobic ionic liquids containing bis(trifluoromethanesulfonyl)imide, [NTf₂]⁻, anions partially dissolve in aqueous phases. The potential ecotoxicity of [NTf₂]⁻ means wastewater streams must be closely monitored to avoid environmental release. A new ion chromatography method is presented, which improves on existing techniques and methods by significantly decreasing analysis time and improving chromatographic peak properties. Consequently, the limit of detection is lowered to 5 μM (1.4 ppm) and limit of quantification lowered to 30 μM (8.5 ppm). The method is reproducible and has a high precision for short and medium chain length ionic liquids (RSD = 0.95%); however, microemulsion effects increase measurement errors for long chain ionic liquids (RSD = 2.32%), albeit by a relatively small amount. Hence, the method is a highly accurate analytical method for highly polarizable [NTf₂]⁻ anions, and quantification in the presence of high salinity samples, such as seawater, is readily achieved. Importantly, this method is a significant improvement on existing techniques (chromatography, NMR, UV-Vis) for many reasons, making it ideal for environmental monitoring or process design of [NTf₂]⁻ ionic liquid-based applications.