PFAS Interference or Contamination?

PFAS contaminants are everywhere in the world and, what is more concerning, in everyone. Recently, I came across an article describing the extent of the problem and that PFAS can be found in nearly all living humans (European teenagers are high – on PFAS – ChemSec). The statement in the article that most resonated with me was this: “In general, we don’t have a solution on how to stop the exposure to PFAS, as they are so persistent in the environment and humans.”

This gives us a better understanding why contamination with PFAS can be found all over our lab, vials, or other sample prep products. During method development, many analysts must address whether it is even possible to get a clean blank below the method detection limit (MDL). 

In this blog I would like to address another problematic PFAS. Recently our technical service group talked to many customers who reported contamination of 6:2 fluorotelomer sulfonic acid (6:2 FTS) and its surrogate sodium 1H,1H,2H,2H-perfluoro-1-(1,2-13C2)-octane sulfonate (M2-6:2 FTS) in variety of products (vials, SPE cartridges, and syringe filters). Our scientist tested all the products but were not able to confirm the contamination. Tested vials (catalog # 23246), SPE cartridges (catalog # 28470), and syringe filters (catalog # 23987) were not contaminated with 6:2 FTS.

So, what were our customers seeing? It appears that the EPA has already solved the problem. EPA method 8327¹ section 4.5 describes why labs may be detecting bias high for the 6:2 FTS and how to go around it:

“High concentrations of the native 4:2 FTS, 6:2 FTS, and 8:2 FTS target analytes will interfere with the primary product ion signals listed in section 17.0, Table 2 for the M2-4:2 FTS, M2-6:2 FTS and M2-8:2 FTS surrogates. This interference results from the natural abundance of the 34S isotope (~4.2% abundance relative to 32S) in the native FTS target analytes and can lead to high bias recovery of these surrogates. Using the secondary product ions identified in Table 2 for quantitation of these surrogates will minimize this interference because this surrogate product ion loses the 13C2-labeled fluorocarbon sidechain to produce 32SO3H- (m/z 81), while the 34S isotope of the target analyte produces 34SO3H- (m/z 83) from the same nominal mass precursor ion.” Using the m/z 81 product ion for quantitation of M2-4:2 FTS, M2-6:2 FTS, and M2-8:2 FTS will reduce interferences from high concentrations of the respective native target analytes compared to the primary ions. Example: use m/z 429/81 for the M2-6:2 FTS surrogate, and not m/z 429/409. “

(EPA method 8327, section 17.0, table 2
8327.pdf (epa.gov)

We reviewed other available methods for the determination of PFAS and how they are treating the fluorotelomer bias. Here are our findings:

Methods	Compound	1st MRM Transition	2nd MRM Transition	Comments
EPA 1633 (2nd Draft method, June 2022)	M2-6:2 FTS	429.1 → 80.9 (parent ion → quantification ion)	429.1 → 409.0 (parent ion → confirmation ion)	Switched quant ion and qual ion for labeled compound and analyte.
	6:2 FTS	427.1 → 407.0 (parent ion → quantification ion)	427.1 → 80.9 (parent ion → confirmation ion)
EPA 533	M2-6:2 FTS	429 → 409 (precursor ion → product ion)	n/a	1st transition only for both analyte and labeled ISTD. No mention of interference nor second transition to monitor
	6:2 FTS	427 → 407 (precursor ion → product ion)	n/a
EPA 8327	M2-6:2 FTS	429 → 409 (precursor → primary product ion)	429 → 81 (precursor → secondary product ion)	No 2nd transition for labeled M2-6:2 FTS in their 2019 edition but added 2nd transition in their 2021 edition. Mentions recovery limits of 70 – 130% might be too narrow for M2-6:2 FTS and some other compounds and the use of m/z 81 for quantitation can reduce the interference.
	6:2 FTS	427 → 407 (precursor → primary product ion)	427 → 81 (precursor → secondary product ion)
EPA OTM-45	M2-6:2 FTS	429 → 409 (precursor ion → primary product ion)	429 → 81(precursor ion → secondary product ion)	No 2nd transition for 6:2 FTS.
	6:2 FTS	427 → 407 (precursor ion → primary product ion)	n/a
ISO 21675:2019	M2-6:2 FTS	429 → 409 (precursor → quantifier)	429 → 81 (precursor → qualifier)	No switching quant ion and qual ion.
	6:2 FTS	427 → 407 (precursor → quantifier)	427 → 81 (precursor → qualifier)
ASTM D7979-20	M2-6:2 FTS	429 → 408.9 (primary transition)	n/a	No 2nd transition for labeled M2-6:2 FTS.
	6:2 FTS	427 → 406.9 (primary transition)	427 → 80.9 (confirmatory transition)
ASTM D7968-17a	M2-6:2 FTS	429 → 408.9 (primary transition)	n/a	No 2nd transition for labeled M2-6:2 FTS.
	6:2 FTS	427 → 406.9 (primary transition)	427 → 80.9 (confirmatory transition)

**Note that the methods are being constantly updated. Always work with the latest version.

¹Method 8327: Per- and Polyfluoroalkyl Substances (PFAS) by Liquid Chromatography/Tandem Mass Spectrometry (LC/MS/MS)