Cyclosiloxane artifacts explain reported Henry's law constants for nonvolatile fluorotelomer sulfonates

The Henry's Law partition coefficient (K_H) is important for understanding and predicting the air-water partitioning and transport of molecules, including per- and polyfluoroalkyl substances (PFAS). Henry's Law constants for three fluorotelomer sulfonates (FTSs) were reported in 2022 by static headspace analysis coupled with gas chromatography (GC)-tandem mass spectrometry. However, FTSs are nonvolatile at the reported experimental pH values (5.0-7.0). We tested the hypothesis that artifacts were responsible for the chromatographic peaks attributed to FTSs. Static air-water partition experiments and controls were conducted with free-acid (neutral) FTS standards with GC-quadrupole time-of-flight mass spectrometry (QTOF). Free acid standards of FTSs directly injected into the GC-QTOF gave no peaks. In contrast, a 10:2 FTOH standard produced a distinct peak and strong match with the NIST23 library. Although FTS homologs are not in the NIST library because they are nonvolatile, accurate mass fragments and formula calculations confirmed that the peaks previously attributed to FTSs were D3, D4, and D5 cyclosiloxanes (74-90 % match). Controls revealed that injection of oxygen and moisture creates the cyclosiloxanes artifacts that were misidentified as FTSs.