Evaluation of different plasma conditions and resolutions for understanding elemental organophosphorus analysis via GC-ICP-SF-MS

Abstract

The state-of-the-art electrolyte in lithium ion battery application is composed of a solvent mixture of organic carbonates and lithium hexafluorophosphate (LiPF₆) as the conducting salt. Decomposition reactions of the hexafluorophosphate anion with the organic carbonates and trace amounts of water in the system result in a large variety of organofluorophosphates. The toxicity of organofluorophosphates has been known for some time and is now drawing interest in the battery research context. Molecular standards are not available as these compounds are supposedly highly toxic, generally unknown or just recently described. Therefore, in this study, the organophosphates formed were investigated with gas chromatography-inductively coupled plasma-sector field-mass spectrometry (GC-ICP-SF-MS). With this setup, it was possible to overcome the need for molecular standards and to perform quantification after separation of species using only one external standard. Comprehensive data of the phosphorus signals were evaluated in different resolution modes (R > 300 and R > 4000) and under different plasma conditions (wet and dry). Thereby, possible interferences originating from aerosol entry, GC solvents, sample matrix or decomposition products could be detected and evaluated. The developed phosphorus speciation procedures and tuning techniques were interrelated. Detection and quantification limits were determined for all setups and additionally, preliminary qualitative and quantitative investigations of different commercially available electrolytes after thermal treatment are presented.