A Systematic Evaluation of Factors Resulting in Incomplete Recovery when Implementing the Adsorbable Organic Fluorine (AOF) and Extractable Organic Fluorine (EOF) Methods

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Per- and polyfluoroalkyl substances (PFASs) are a global environmental contaminant of concern whose persistence in water systems is associated with negative effects on human health. The typical way for measuring PFAS concentrations in environmental samples is by means of liquid chromatography-mass spectrometry (LC-MS), but authentic analytical standards are only available for a few dozen out of thousands of individual PFAS species. Therefore, techniques that quantify total organic fluorine (TOF) are important for PFAS risk assessments. Adsorbable organic fluorine (AOF) and extractable organic fluorine (EOF) are techniques for measuring TOF. Both techniques rely on the loading of PFASs onto either activated carbon (AOF) or a WAX adsorbent (EOF) followed by a washing step to remove residual inorganic fluoride from the adsorbent. The EOF method also has an elution step that results in the transfer of captured PFASs to a small volume of an organic solvent. Both methods are completed with a combustion step to mineralize the PFASs and capture the evolved hydrogen fluoride for quantification; the AOF method performs the combustion on the washed activated carbon and the EOF method performs the combustion on the organic solvent eluate. The objective of this study was to systematically evaluate each step of the AOF and EOF methods for the recovery of a set of ten ultrashort-, short-, and long-chain perfluoroalkyl acids. We measured the overall recovery of fluoride for each method for each of the PFASs, and the recovery of fluoride and each PFAS around the loading, washing, and elution steps. We also measured the combustion efficiency of each PFAS by means of direct combustion without sample preparation. The overall AOF recovery ranged from 9.3% – 103.3% and the overall EOF recovery ranged from 21.0% – 108.1%, with higher recoveries generally measured for PFASs with increasing chain length in both methods. The three ultrashort-chain PFASs exhibited the lowest overall recoveries from 9.3 – 25.2% for AOF and 21.0 – 51.5% for EOF. Our systematic evaluation of each step in the AOF method revealed that decreases in the overall recovery are primarily the result of the loss of ultrashort- and short-chain PFASs during the washing step and the incomplete mineralization of perfluoroalkyl sulfonic acids (PFSAs) during combustion. Our evaluation of each step in the EOF method revealed that decreases in the overall recovery are primarily the result of the incomplete elution of short- and long-chain PFASs and the loss of ultrashort-chain PFASs during the washing step. Together, our experiments suggest that the EOF method is more appropriate than the AOF method for measuring TOF in samples containing significant fractions of ultrashort- and short-chain PFASs and that significant methodological improvement are possible with a focus on the washing, elution, and combustion steps.

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109 pages


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Helbling, Damian

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Reid, Matthew

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Civil and Environmental Engineering

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M.S., Civil and Environmental Engineering

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Master of Science

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dissertation or thesis

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