On the Unimolecular Breakdown Products of Short Deprotonated Per‐ and Poly‐Fluorinated Acids and Alcohols
Bibliographic record
Abstract
ABSTRACT The strong C–F bond found in per‐ and poly‐fluorinated alkyl substances (PFAS) makes them resistant to degradation and thus persistent in the environment. One of the most common methods for quantifying PFAS in environmental matrices is to use tandem mass spectrometry. However, the dissociation of ions made by deprotonating PFAS alcohols and acids has only been qualitatively explored. In this study, we investigated the breakdown of deprotonated 2,2,3,3,3‐pentafluoropropionic acid (1, m/z 163), 3,3,3‐trifluoropropionic acid (2, m/z 127), 2,2,3,3,3‐pentafluoro‐1‐propanol (3, m/z 149), 3,3,3‐trifluoro‐1‐propanol (4, m/z 113), and trifluoromethanesulfonic acid (5) by energy‐resolved collision‐induced dissociation (CID) tandem mass spectrometry and density functional theory (M06/6‐311+G(d,p)). Ion 1 loses CO2 at low lab‐frame collision energy. Ion 2 also loses CO2 to form the 1,1,1‐trifluoroethane ion (m/z 83) and 1,2‐difluoroethylene to form FCO2− (m/z 63). RRKM calculations for the two reactions show that m/z 83 has a higher entropy of activation driving its formation. Ion 3 undergoes the loss of CH2O to form the pentafluoroethyl anion (m/z 119) and the loss of HF to form CF2CF2COH− (m/z 129). Ion 4 produced four fragment ions with two primary reactions making CF3CHCH− (m/z 95) + H2O and CF2CHCOH2− (m/z 93) + HF, which go on to dissociate further to produce CF3− (m/z 69) + HCCH + H2O and CF2CH− (m/z 63) + CH2O + HF. At low collision energy, m/z 95 dominates due to a lower energy transition state, but as internal energy increases, m/z 93 takes over as its transition state has a more favorable entropy. Ion 5 produced FSO3− (m/z 99), SO3− (m/z 80), and CF3− (m/z 69). SO3− was the most abundant fragment due to its higher electron affinity.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.003 | 0.001 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".