Determination of residual chloride content in ionic liquids using LA-ICP-MS

Abstract

Nowadays, ionic liquids (ILs) are used in a wide range of applications. Their exceptional chemical and physical properties, sustainability of use and the possibility of easy recycling are attractive aspects promoting the acceptance of ILs also for commercial applications. While synthesis is in most cases simple and straightforward, purification of the reaction products might pose a number of problems. Due to the major influence of inorganic contaminations from the synthesis process, thorough monitoring of impurities is required. However, the unusual properties of ILs create some problems for conventional chemical analysis. In this work, a dried droplet approach with subsequent LA-ICP-MS sampling will be used for the analysis of chloride in ILs – a by-product from the synthesis procedure. Dried droplet application onto pre-cut filter paper disks allows the analysis of hydrophilic as well as hydrophobic ILs with calibration from dried aqueous standards for signal quantification. The approach is applied on two types of alkylimidazolium ILs, underlining the versatility of the sample preparation and measurement approach. Compared to commonly used analysis techniques for chloride in ILs, the presented approach is simple, fast, and does not require harmful reagents. Different internal standardization strategies were investigated during this study. With a reproducibility of below 2% relative standard deviation and limits of detection of 0.09 mg g⁻¹ for chloride in ILs, the presented approach was showed to be fit for the purpose of routine analyses and reaction monitoring. If necessary, the approach can be extended to other analytes of interest in the field of the synthetic chemistry of ILs.