Detection of perfluoroalkyl carboxylic acid (PFCA) dimers in ion mobility spectrometry: using CCS-m/z trendlines to suggest their gas-phase conformation

Per- and polyfluoroalkyl substances (PFASs) are emerging pollutants of great concern, with over 5,000 compounds currently reported. Hyphenated techniques such as ion mobility spectrometry (IMS) coupled to LC-HMRS hold promise for non-targeted screening of these substances. Among the many advantages of IMS, a descriptor related to molecular shape is obtained through the collision cross-section (CCS) which provides an additional identification point. However, when trapped IMS (TIMS) is coupled to LC-MS to analyze legacy perfluoroalkyl carboxylic acids (PFCAs), multiple mobility peaks are observed at the m/z of a single deprotonated ion ([M-H]-), preventing the determination of an unambiguous CCS as an identifier. This works aims to assign these multiple peaks and use their CCS-m/z trendlines to have insight into their gas-phase conformation.