While not currently regulated, ultrashort-chain (C2–C3) per- and polyfluoroalkyl substances (PFAS) are of great interest. Current testing methodologies using reversed-phase liquid chromatography (LC) columns cannot be used because of a lack of retention, so either a separate method or a different column is required.
A unique, hybrid ion-exchange/HILIC column (Raptor Polar X) was used to develop a comprehensive LC–MS/MS method for the analysis of ultrashort-chain through long-chain, and alternative PFAS in water sources (tap, river, groundwater, and sewage effluent). The Raptor Polar X‘s multimode retention mechanisms allow for retention with a single isocratic run.
Chromatographic conditions are reported in Figure 1.
To avoid introducing background contamination, polypropylene vials and caps were used during sample preparation.
Each water sample of 250 μL was mixed with 250 μL of methanol and 5 μL of internal standard solution (10 ng/mL of 13C2-PFHxA, 13C2-PFOA, 13C3-PFBS, 13C4-PFOS in methanol).
Calibration standards were prepared by using deionized water and fortified with 14 analytes (see Figure 1) at a range of 10–800 ng/L. The calibration standard solutions were diluted 1:1 as above.
A Restek tap water sample, along with three water samples (river, ground, and sewage effluent) supplied by the United States Environmental Protection Agency were fortified at 40 and 160 ppt. Blank and fortified water samples were diluted 1:1 in methanol as above for chromatographic analysis. For TFA measurement in groundwater, the sample was diluted fivefold with deionized water before fortification due to its high TFA concentration.
All analytes were eluted in 4 min with good peak shapes (Figure 1). The overall analytical cycle time was 8 min to ensure no matrix-related interferences.
Method linearity from 20–800 ppt for trifluoroacetic acid (TFA) and 10–800 ppt for all other analytes provided r2 values >0.996 and deviations <20% using a 1/x weighted quadratic regression.
Samples were fortified at the low and high concentrations of their calibration ranges and run in duplicate for each analytical batch. A total of three batches were measured on different days. Concentrations of fortified samples were adjusted to account for any observed background contamination in sample blanks. Results are presented in Table I.
These results demonstrate that switching to a mixed-mode LC column provides the capability to analyze currently monitored and emerging PFAS contaminants in a single, short, isocratic run, preparing laboratories for the future of PFAS testing.
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