Online and large volume injection techniques for trace analysis of per- and polyfluoroalkylated substances
Creators: name: Miller, Ashley
Publisher: name: University of Tasmania
Year: 2024

description: Per- and Polyfluoroalkylated Substances (PFAS) are a class of anthropogenic environmental pollutants distinguished by the presence of a partial or fully fluorinated fluoroalkyl chain. They possess both hydrophobic and lipophobic properties along with high chemical stability and have been utilised widely in industrial and commercial sectors. This widespread usage has resulted in their distribution into the environment where they persist due to resistance to breakdown. Numerous human health effects have been correlated to PFAS exposure resulting in the necessity for routine monitoring of these compounds. Routine monitoring of environmental pollutants is typically performed within commercial and government analytical laboratories. Emphasis is placed on method robustness, to meet regulatory guidelines, and to enable extraction and analysis to be performed in a repeatable and reliable fashion.<br>Advances in analytical instrumentation such as mass spectrometry have allowed for rapid advances in the speed, selectivity, and sensitivity of the analysis. However, advances in sample preparation procedures required prior to analysis to extract analytes into a suitable form for injection and to remove interfering matrix components, have lagged behind with sample extraction often the bottleneck when performing analysis of environmental contaminants in matrices such as soil, water, and biota. Uncertainty surrounding the human health impacts of PFAS exposure necessitates quantitation at low ng/L levels. Therefore, for analysis of PFAS in water, Solid Phase Extraction (SPE) is typically performed.<br>Much of recent analytical chemistry research has been directed towards the development of miniaturised, automated, and hyphenated (where extraction is directly coupled to detection without the need for user input) techniques. In this work Online SPE was applied to a selection of PFAS which form the suite of analytes routinely monitored by a commercial analytical laboratory with the aim of demonstrating that the technique is a viable alternative to the manual offline approach. A key requirement is demonstrating equivalent method performance characteristics, namely LOQs (target 1 ng/L) and capacity to analyse complex water matrices such as ground and wastewater with equivalent method performance.<br>Initially an online method utilising a mixed mode C18/WAX SPE column in conjunction with a reversed phase C18 analytical column was developed. The method evidenced the capacity to reach the targeted quantification limits with injection of 500 µL of deionised water. However, the injection of more complex water samples caused significant detrimental impacts on the quality of the analytical data and, chiefly, evidenced appreciably poorer performance compared to the offline approach. To improve the analytical performance a new method was developed utilising a polymeric (polystyrene divinylbenzene) WAX SPE column in conjunction with a reversed phase C18 analytical column for separation. The analyte list was expanded to 39 PFAS in line with newly available analytical standards. This approach exhibited substantially improved performance when applied to complex water samples enabling a close comparison between performance metrics of the offline and online approaches. The analysis evidenced that equivalent, and in some instances superior, performance could be obtained in regard to limits of detection and quantification, quantification of samples containing incurred PFAS at ≤10 ng/L concentrations, and matrix effects in challenging sample types such as those with high conductivity and organic content. The method also developed and elucidated strategies for mitigating issues surrounding PFAS system contamination when performing online SPE.<br>Additionally, the technique of LV-DI was applied to the trace level analysis of fluorotelomer alcohols (FTOHs) in water. A method utilising LC-MS/MS coupled to APCI was developed to enable trace level analysis of FTOHs in water via direct injection. To provide quantification limits in line with what can be achieved via SPE LV-DI was applied. To prevent adsorption of long chain FTOHs to autosampler vials the addition of 50% organic solvent to the sample was required, necessitating that the sample was diluted back to aqueous conditions to enabling refocusing on the analytical column. This approach enabled quantification at low ng/L concentrations via injection of 300 µL of sample in a 15 min run time without recourse to any sample pre-treatment steps. By comparing the matrix effect between injection of 30 µL and 300 µL it was evidenced that the increased injection volume was not accompanied by commensurate increase in matrix effects demonstrating the potential for this technique to be applied more broadly to PFAS analysis.<br>