Methylation in ambient ion source enables direct isomer differentiation of oligosaccharides by tandem mass spectrometry
Bibliographic record
Abstract
Oligosaccharides are carbohydrate polymers with prebiotic, immunomodulatory, and antimicrobial activities. However, their structural complexity makes it challenging for characterization. In this work, we demonstrated a powerful instant in situ methylation approach to derivatize oligosaccharides with tetramethylammonium hydroxide (TMAH) in an ambient ion source known as direct analysis in real time (DART). The reaction occurs instantaneously when the sample and TMAH mixture is bombarded by excited-state helium from the DART source, and the methylated species are simultaneously charged through the Penning process. Mass spectrometry (MS) showed the formation of partial, full, and per-methylation products, along with methylated saccharide fragments. Unique fragmentation patterns can be generated because of the enhancement on the structural differences of isomers when fully or partially methylated. By using accurate mass and tandem MS (MS/MS), we demonstrated that trisaccharide and pentasaccharide isomers with subtle structural variations produced distinctively characteristic fragment ions. Isomeric saccharides in mixtures were qualitatively identified, and trisaccharide isomers in real samples were quantified. Varying degrees of polymerization of oligosaccharides, and their stereochemical and other isomeric differences were directly characterized. This method is significantly simpler compared to currently used workflow, and the time-consuming chromatographic separation step was eliminated.
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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) | 0.001 | 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 | 0.001 |
| Open science | 0.000 | 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".