Feasibility of closing the PFAS mass balance: exploring the potential of liquid sampling atmospheric pressure glow discharge (LS-APGD) with Orbitrap mass spectrometry for neutral PFAS†

Per- and polyfluoroalkyl substances (PFASs) are anthropogenic compounds of high toxicological impact. Routine PFAS analysis is limited to a few dozen compounds from the more than 12 000 registered ones; the vast majority of them cannot be included in the analysis due to ionisation challenges. The liquid sampling-atmospheric pressure glow discharge (LS-APGD) source has been explored in a wide variety of mass spectrometric techniques, proving its versatility. PFASs have recently been included in the scope of analysis. In this study, we used LS-APGD to analyse several different PFAS forms, including some that can be done routinely, and others that are still challenging. The results show that not only the analysis of more-or-less routine PFAS compounds is possible, but LS-APGD also shows potential for analysing neutral, semi-volatile PFASs as well as unfunctionalized fluorocarbons (perfluoroalkanes). Admittedly, further optimisation is necessary to achieve the required analytical target concentrations. Comparing ski wax extracts to standards suggests that the sample matrix may influence (in this case in a positive way) the signal intensity, which needs to be taken into account in the data analysis process. Plasma discharge conditions have been optimised using a design of experiments approach. This marks the first systematic optimisation of LS-APGD in negative ionization mode for a wide variety of organic compounds. In addition, this is the first instance that LS-APGD has been shown to operate with nonpolar solvents. The body of work presented in this manuscript represents a significant expansion of the capabilities of the already versatile LS-APGD ion source.