Stability of volatile organic compounds in thermal desorption tubes and in solution
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Bibliographic record
Abstract
Exhaled breath volatile organic compounds (VOCs) are often collected and stored in sorbent tubes before thermal desorption-gas chromatography-mass spectrometry (TD-GC-MS) analysis. Information about the stability of VOCs during storage is needed to account for potential artifacts and monitor for losses. Additionally, information about the stability of VOC standards in solution is required to assess their performance as quality control and internal standards. We evaluated the stability of a standard mixture of 42 VOCs in dual-sorbent tubes containing Tenax® TA and Carbotrap 1TD over 60 d at commonly used storage conditions: room temperature (∼21 °C), 4 °C, and -80 °C. The same 42 VOCs were also evaluated for their stability in methanol over 60 d while stored at -20 °C. All samples were analyzed using TD-GC-MS. During storage, most VOCs were stable on sorbent after 60 d: 36/42 (86%), 39/42 (93%), and 41/42 (98%) had not statistically changed for room temperature, 4 °C and -80 °C, respectively, based on Spearman rank correlation coefficients and linear regression analysis. The isotopically labeled VOCs tested here are well-suited to serve as internal standards for pre-analysis or storage. Degradation of VOCs in solution was apparent after 60 d: 27/42 (64%) of VOCs had statistically decreased. The total VOC mixture had dropped to 90% of its original intensity after ∼22 d and a subset of VOCs typically used as internal standards dropped to 90% in ∼16 d. Analysts using similar mixtures should make a fresh solution at least every two weeks to ensure analytical accuracy. This study provides important insights into storage practices for both sorbent tubes and standard solutions, guiding analysts toward improved reliability and accuracy in exhaled breath analysis.
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Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 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 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
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 it