We are pleased to offer a sensitive and specific isotope dilution LC-MS/MS method for the measurement of Trifluoroacetic Acid (TFA) and 4 other ultrashort perfluoroalkyl carboxylates and sulfonates. Our method measures these targets at low ng/L from an EPA 1633 extract meaning the same sample can now be used to generate both 1633 data and ultrashort PFAS. This release is part of our ongoing push to expand our PFAS target list past one hundred by the end of 2023!
Background
Per-and Polyfluoroalkyl Substances (PFAS) with chain lengths of 3 or fewer are referred to as ultra-short PFAS and there is a significant data gap on their occurrence, fate and toxicity information. Ultra-short PFAS of particular interest include trifluoroacetic acid (TFA), pentafluoropriopionic acid (PFPrA) and corresponding sulfonic acids trifluoromethane sulfonic acid (PFMS), and the C2 and C3 perfluorinated sulfonic acids PFEtS and PFPrS. These acids have multiple sources in the environment with TFA arising from atmospheric degradation of hydrofluorocarbons (HFCs and HCFCs) such as the ubiquitous refrigerant HFO-1234yf, the oxidation and chain shortening of fluorotelomer and other PFAS. PFPrA is also likely formed from the degradation of fluorotelomer PFAS. PFMS is used widely in organic synthesis and in lithium ion batteries. The limited information on TFA available in the literature suggests that background concentrations are steadily increasing and a recent study on occurrence showed levels of up to 140 μg/L in tap water. LC-MS/MS methods used for short and long-chain PFAS do not typically work for ultra-short PFAS necessitating new approaches for analysis.
The Target List
| PFAS | Short Name | Formula | CAS # |
| Carboxylates | |||
| Trifluoroacetic acid | PFEtA or TFA | CF3-COOH | 76-05-1 |
| Pentafluoropropionic acid | PFPrA | CF3-CF2-COOH | 422-64-0 |
| Sulfonates | |||
| Trifluoromethanesulfonic acid | PFMeS | CF3-SO3H | 1493-13-6 |
| Pentafluoroethanesulfonic acid | PFEtS | CF3-CF2-SO3H | 354-88-1 |
| Heptafluoropropanesulfonic acid | PFPrS | CF3-CF2-CF2-SO3H | 423-41-6 |
The Method
We have now developed and validated an LC-MS/MS method for aqueous samples that uses an alternate LC column ideally suited for ultrashort PFAS. Many of these PFAS show marginal/poor performance under typical 1633 conditions and TFA is not compatible at all. Using our new column approach enables good chromatography and low reporting limits for the ultrashorts starting at 20 ng/L for TFA and 1-2 ng/L for the other targets. The method has been designed carefully to ensure broad compatibility with EPA 1633 Draft. We can run a separate portion of the extract from 1633 preparation enabling the reporting of the list of 40 1633 PFAS and these additional ultrashort PFAS from the same sample.
