Analysis of perfluoroalkyl anion fragmentation pathways for perfluoroalkyl carboxylates and sulfonates during liquid chromatography/tandem mass spectrometry: evidence for fluorine migration prior to secondary and tertiary fragmentation
Bibliographic record
Abstract
It is known that under liquid chromatography/electrospray tandem mass spectrometry (LC/ES-MS/MS) conditions, the perfluorocarboxylate anion [R(F)CO(2)](-) first loses CO(2) to give a perfluoroalkyl anion R(F)(-), [(M-H)-CO(2)](-), which can subsequently fragment to give inter alia lower mass carbanions. It has been suggested in a previous study that such secondary fragmentation involves cleavage of C(n)F(2n) segments. Our study of the LC/ES-MS/MS of a series of (13)C-labeled perfluoroalkyl carboxylic acids (PFCAs) indicates that fragmentation of the R(F)(-) anion does not involve simple 'unzipping' of a primary perfluoroalkyl anion of the type F(3)C(CF(2))(x)CF(2)(-). For example, we have discovered that the secondary transition for the mass-labeled PFOA, perfluoro-1,2,3,4-(13)C(4)-octanoic acid (MPFOA), gives two signals of equal intensity at m/z 169 and 172. We propose a mechanism of fragmentation that involves rapid fluorine shifts, after the initial decarboxylation, which generate a series of new anions prior to secondary and tertiary fragmentation.
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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 | 0.001 | 0.001 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.002 | 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".