Coupling Liquid Chromatography to Orbitrap Isotope Ratio Mass Spectrometry: Overcoming Isotope Effects of Chromatography and Amount-Dependency by Peak Homogenization
Bibliographic record
Abstract
High Resolution Image Download MS PowerPoint Slide Electrospray ionization Orbitrap mass spectrometry (ESI-Orbitrap-MS) has recently proven to be a powerful tool for compound- and position-specific stable isotope analysis, targeting isotopologues of multiple elements (H, C, N, O, S) in polar analytes. However, studies have so far mainly focused on pure analyte solutions via direct infusion. Here, we present the online coupling of liquid chromatography (LC) to ESI-Orbitrap-MS for stable isotope analysis of sulfamethoxazole (SMX), a synthetic antimicrobial, used as a model compound. Our study explored the fidelity of isotope values with two strategies for capturing and broadening chromatographic peaks after LC. When capturing the target analyte in a capillary (0.7 mm inner diameter), peak shape was retained, resulting in systematic deviations in isotope values caused by isotope effects from chromatography of up to 70‰ and amount-dependency of up to 65‰. A dynamic mixing chamber was used to homogenize the target analyte upon elution, removing these deviations and resulting in stable carbon, nitrogen, and sulfur isotopologue ratios in various fragments of sulfamethoxazole across the chromatographic peak. Comparison with data from conventional magnetic sector isotope ratio mass spectrometry successfully calibrated the setup for carbon and sulfur isotope ratio analysis. This resulted in a precision for δ 13 C within the isoxazole moiety from SMX of 1.5‰ (95% confidence intervals CIs derived from uncertainties of sample ( n = 4) and reference ( n = 5)), and for δ 34 S in the SO 2 fragment of 0.9‰ (95% CI, derived again from uncertainties of sample ( n = 4) and reference ( n = 5)). This work paves the way for the online coupling of LC to ESI-Orbitrap-MS in future compound- and position-specific stable isotope analyses across various research fields.
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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 | 0.005 |
| Meta-epidemiology (narrow) | 0.002 | 0.001 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.002 |
| Research integrity | 0.002 | 0.002 |
| 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".