Evaluating MTBSTFA derivatization reagents for measuring naphthenic acids by gas chromatography-mass spectrometry
Bibliographic record
Abstract
Naphthenic acids (general formula CnH2n+ZO2) are found in petroleum and oil sands deposits. Release of these acids to aquatic environments is a concern because of their potential toxicity. Naphthenic acids consist of a complex mixture of carboxylic acids, and estimating their concentrations in environmental samples is a challenge. Two recent reports have described gas chromatography-mass spectrometry (GC-MS) methods to selectively detect these acids in fish flesh and water samples. The methods use N-methyl-N-(t-butyldimethylsilyl)-trifluoroacetamide (MTBSTFA) with 1% t-butyldimethylchlorosilane (t-BDMCS) to derivatize naphthenic acids to their t-butyldimethylsilyl derivatives. Single ion monitoring (SIM) was used to detect the fragment m/z 267, which corresponds to the derivatives of one isomer class (n = 13 and Z = −4) of naphthenic acids. The SIM chromatograms give a characteristic naphthenic acids hump between retention times 15 and 20 min and a sharp peak for the t-butyldimethylsilyl derivatized surrogate standard, 9-fluorenecarboxylic acid. Integration of this hump and the peak from the surrogate standard allows quantification of the naphthenic acids. Using newly purchased MTBSTFA containing 1% t-BDMCS (from three different suppliers) yielded SIM chromatograms with one or two large contaminating peaks (eluting at 16.7 and 18.8 min) that interfered with integration of the hump, rendering the method unreliable. The contaminants were traced to the presence of t-BDMCS. Each of the three suppliers sells MTBSTFA devoid of t-BDMCS, and using MTBSTFA without 1% t-BDMCS was found to be suitable for the GC-MS method.
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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 | 0.003 | 0.003 |
| Meta-epidemiology (narrow) | 0.001 | 0.001 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.001 | 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".