Ion chromatographic determination of structurally varied ionic liquidcations and anions—a reliable analytical methodology applicable to technical and natural matrices

Abstract

An ion chromatographic system with conductometric detection was used to analyse a broad structural variety of ionic liquid (IL) cations and anions. The selection of cationic entities covered the chemical space of IL cations as comprehensively as possible and contained the most common head groups substituted with different alkyl- and functionalized side chains. Also investigated was a set of commonly used IL anions showing a relatively wide polarity range, from comparatively hydrophilic species (e.g.dicyanimide and tetrafluoroethanesulfonic acid) to moderately hydrophobic entities (e.g.(CF₃SO₂)₂N⁻ or B(CN)₄⁻) and to the strongly hydrophobic trifluorotris(pentafluoroethyl)phosphate anion (((C₂F₅)₃PF₃)⁻). The separation of these IL constituents from inorganic matrix-forming ions (Li⁺, Na⁺, K⁺, Mg²⁺, Ca²⁺ or F⁻, Cl⁻, Br⁻, SO₄²⁻, HPO₄²⁻) was achieved for all 30 tested IL structures, depending on the eluent used. Activated sludge samples from biodegradation experiments were chosen for a case study in order to illustrate the performance and the usefulness of the methods developed. The separation and quantification of traces of IL ions in the presence of large numbers of inorganic ions and high organic matrix loads were demonstrated. In general, the analytical system and its associated methods appear to be widely applicable to a broad range of IL structures as well as different technical and natural matrices.