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A. Limbeck, M. Bonta, T Anderl, A. Cognigni, M. Hejazifar, K. Schröder:
"Determination of inorganic contaminants in ionic liquids using Laser-Ablation-Inductively-Coupled-Mass-Spectrometry (LA-ICP-MS)";
Vortrag: 26th EUCHEM Conference on Molten Salts and Ionic Liquids, Vienna, Austria; 03.07.2016 - 08.07.2016; in: "26th EUCHEM Conference on Molten Salts Ionic Liquids", (2016), ISBN: 978-3-9504017-4-5; S. 128.

Chemical and physical properties of ionic liquids could be altered by prevailing impurities. To assure the required behavior and to avoid unwanted negative effects, for example changes in melting point or deactivation of catalysts, adherence of defined contamination levels is mandatory. For the determination of inorganic contaminants mostly wet chemical methods such as titrimetric approaches are used in lab-routine, but limitations in selectivity and sometimes also sensitivity hamper universal application. Improved detection methods include ion chromatography, X-ray fluorescence or atomic spectroscopic techniques. These methods offer higher sensitivity and accuracy compared to classical wet chemical methods; however, they lack in ease of use and often require sophisticated sample preparation.
In this work, an alternative approach for the analysis of residual inorganic contaminants in ionic liquids is presented. The procedure is based on a preliminary dilution of the sample with ethanol to simplify further sample handling. After deposition of a sample droplet on a pre-cut filter paper disk, the solvent is smoothly evaporated, and finally the filter disk including the applied ionic liquid is analysed using LA-ICP-MS. After thorough optimization, the developed approach enables external calibration using aqueous standard solutions, and thus offers a simplified method for accurate quantification of inorganic contaminants in ionic liquids. Further advantages are the low volume of sample solution required for analysis and high sample throughput.
Applicability of the presented LA-ICP-MS method is demonstrated by the determination of residual chloride in two different types of ionic liquids. The excellent sensitivity achieved (detection limit of 0.1 mg g-1) allowed reliable analysis of the remaining chloride content even after multiple washing steps, facilitating assessment of removal efficiency.

LA-ICP-MS, ionic liquids, residual chloride, quantitative analysis