Formatted Title
Beyond 40: Extended Targeted PFAS Monitoring past EPA Method 1633
Background/Objectives
The EPA 1633 Draft method has standardized on a list of 40 PFAS selected from perfluorinated alkyl acids, C8 sulfonamide PFAS, polyfluorinated alkyl acids and per-and polyfluoroalkyl ethers. While this list represents a good base of PFAAs that are of regulatory interest, and their precursors, it represents a very short subset of PFAS that are present in the environment, especially as shorter chain sulfonamides, phosphate-based PFAS, neutral PFAS such as fluorotelomer alcohols are not present. One of the major challenges with PFAS are their sheer diversity of structure, which makes the design of extended target list methods challenging as any approach needing a pre-concentration step such as solid phase extraction (SPE) for lowered reporting limits is also selective to certain types of PFAS, weak anion exchange (WAX) for example selecting for anionic PFAS. While untargeted approaches can provide a wealth of information on extended PFAS characterization, quantitative information is not available in the absence of a typical target-analysis method. With the objective of increasing quantitative PFAS coverage and extending EPA 1644, we 1) pre-selected nearly 100 PFAS as candidates for an extended monitoring set; 2) developed and validated both direct-injection and SPE LC-MS/MS methods for these PFAS; 3) assessed fit of these specific PFAS to the standard 1633 workflow to build an “extended 1633” list; and 4) analyzed samples from various sources including ambient sites, contaminated sites and waste streams using the “extended 1633 list” to identify areas of easy expansion.
Approach/Activities
We selected PFAS candidates for our study based on literature review of recent untargeted analysis and suspect screening studies and standards availability from commercial vendors. Selected PFAS included chain length extensions for PFAAs to extend the list past C14 PFCA and down to trifluoroacetic acid (TFA), fluorotelomer alcohols, phosphates such as 6:2 DiPAP, AFFF active ingredients, C4-C6 sulfonamides such as FBSA and PFHxSA, ethers such as Nafion BP2 and more. We performed LC-MS/MS method and SPE method optimizations to understand the fit of each of these new PFAS into different analytical approaches. We then assessed the recovery of each of these new targets through the standard EPA 1633 process for water samples.
Results/Lessons Learned
Our study of the nearly 100 PFAS indicated that the PFAS fell into four distinct types. Twenty-six of the new PFAS studied including 6:2 DiPAP and several short chain sulfonamides were reportable through an extended 1633 analysis. Fluorotelomer alcohols could be reported using LC-MS/MS down to low ng/L levels but needed a separate workflow. Ultrashorts such as C2 (TFA), C3 PFCA and C1-C3 PFSA needed a separate instrumental run but were partially compatible with 1633 at a lowered sample size. Several other PFAS such as cationic and zwitterionic AFFF ingredients were not compatible with 1633 and performed best under a direct injection approach. Analysis of samples with this extended target set is ongoing. Preliminary results show that the 1633 approach is widely extensible to targets such as 6:2 DiPAP which are known to be present at high levels in municipal waste effluents/biosolids and our study provides a blueprint for the extension of 1633-type target analysis methods.