Ultrahigh‐performance liquid chromatography–tandem mass spectrometry quantitation of <i>o</i> ‐cresol in hydrolyzed human urine to assess toluene exposure
Bibliographic record
Abstract
RATIONALE: Toluene is a volatile organic compound used in domestic and industrial applications. The main routes of workplace exposure to toluene are inhalation and dermal contact. As toluene exposure can cause severe nervous system damage, its quantification is crucial to prevent occupational illness. Toluene is metabolized mainly as hippuric acid, S-benzylmercapturic acid and epoxides. These are rapidly converted to o-/p-cresol, which is then excreted in the urine as conjugated glucuronides and sulfates. o-Cresol and its conjugates can be chemically hydrolyzed to form free o-cresol, which can then serve as a urinary biomarker of toluene exposure. Current analytical methods for quantifying o-cresol in hydrolyzed urine are, however, either weakened by interference, are not sensitive enough or require water-sensitive sample preparation. Development of a liquid chromatography-tandem mass spectrometry method for assessing exposure to toluene is thus required. METHOD: Urine samples were acidified and heated to form free o-cresol and then derivatized with dansyl chloride and diluted. Extracts were separated by reverse-phase chromatography on a BEH phenyl column and then analyzed using a triple quadrupole instrument in selected reaction monitoring mode. RESULTS: The dansyl chloride derivatization step was optimized to produce the derivative within a reaction time of 3 min. Hydrolysis efficiency in forming free o-cresol from conjugated metabolites was evaluated using o-cresol-β-d-glucuronidespiked human urine: complete hydrolysis occurred in 45 min. Dynamic range was 0.4 to 40 μM, and the method was useful for toluene monitoring in non-occupational (0.1 μmol/mmol creatinine) as well as occupational (0.3 μmol/mmol creatinine) exposure. The calculated limit of detection and limit of quantitation of the method were 0.06 and 0.21 μM, respectively. Intraday and interday precisions were 3.2% and 4.4%, respectively. Method accuracy was established as 99% using ClinChek® urine controls. CONCLUSION: An ultrahigh-performance liquid chromatography-tandem mass spectrometry method for analysis of o-cresol was developed for biological monitoring of toluene exposure in human urine. This is the method of choice used by occupational health and safety practitioners in the province of Québec, Canada.
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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) | 0.001 | 0.001 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 0.000 |
| 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".