A Proxy Test for “Total” PFAS – Organofluorine Analysis – What They Tell You and What They Don’t

Both existing and impending regulations for PFAS have focused on a handful of compounds, like PFOA and PFOS, that are readily found in the environment and have been the subject of many toxicological assessments. However, questions regarding thousands of PFAS with little or no toxicity data have prompted researchers to develop non-compound specific proxy methods intended to represent and estimate “total” PFAS. In general, the techniques we’ll describe exclude most of the smaller chain constituents and the entire class of fluoropolymer PFAS compounds.  These limitations must be considered by data users when making risk decisions. 

Five of the proxy methods for “total PFAS” are total (a misnomer) organic fluorine (TOF), adsorbable organic fluorine (AOF), extractable organic fluorine (EOF), particle-induced gamma ray emission (PIGE), and fluorine-19 nuclear magnetic resonance (19F-NMR). The last two, PIGE and 19F-NMR, are significant contributors to PFAS research, but effectively exist in the realm of academia and will not be discussed here. The other three all incorporate the use of a combustion ion chromatograph (CIC). They each effectively have a different technique for either separating or calculating the organofluorine, and each has its own advantages and disadvantages.  

Only one has risen to the top as a multi-laboratory validated EPA method, and that is AOF, which is limited to the aqueous medium. This is the basis for EPA Method 1621, which was recently published in a final draft. The technique involves passing an aqueous sample across granulated activated carbon (GAC), followed by washing off the inorganic fluoride and combusting an aliquot of the carbon with an ion chromatography (IC) interface, where (total) fluoride is determined, and the results are reported as AOF. The limitation of this aqueous sample technique is that it does not include polymeric PFAS, and many short-chain and very long-chain PFAS do not adsorb efficiently to GAC.  

Another technique being used is EOF. This relies on either a direct methanol extraction for solid samples or a solid-phase extraction (SPE), in aqueous samples.  With either technique, the methanol can be concentrated and, therefore, can achieve lower detection limits than other techniques. This extraction technique can also be applied to non-environmental solid matrices and consumer products.   A portion of the methanol extract is combusted, and using IC, the (total) fluoride concentration is determined, which is reported as EOF. 

Lastly, for one of the available TOF method options, total fluorine and inorganic fluorine are measured in a sample, and then the TOF is calculated as the difference between the two values. In most cases, the total fluorine and inorganic fluorine concentrations are much, much higher than the organofluorine; so, there can be a great deal of uncertainty around the calculated result. Most of the time, this makes the reporting levels higher than the other techniques.  Another limitation of this technique is that it is only applicable to aqueous samples, and it does not include polymeric PFAS. 

A direct, reliable method for the measurement for TOF inclusive of polymeric PFAS, on both aqueous and solid matrices, is currently lacking and sorely needed for application on multi-media environmental samples and consumer products. Our Team is working with ASTM F15.81 and other consensus organizations to design and validate a direct, reliable method for the measurement for TOF. 

We Can Help 

With many speciated and non-speciated PFAS methods and techniques available and investigators trying to answer study questions, having a full-solution partner who can guide you through the process will save time and money, but more importantly, will generate accurate and reliable project data. The PFAS Integrated Solutions team at Montrose Environmental can help you from planning through execution with PFAS solutions that are timely and cost-effective.   

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