A Colorimetric Method for Naked-eye Detection of 6PPD in Rubber Products and Wastes
Bibliographic record
Abstract
N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD) has received increasing attention due to its ubiquitous environmental occurrence and the extreme aquatic toxicity of its quinone oxidation product. Given 6PPD's application as an antioxidant in a wide array of rubber products and wastes, cost-effective measurement of 6PPD is important for product and waste management. We herein developed a naked-eye colorimetric method for the rapid measurement (<10 min) of 6PPD in rubber products and wastes with low cost (<$1 per sample). The inspiration for this method stems from the observation of the formation of red-colored products when 6PPD is exposed to oxidants, at concentrations as low as 0.65 mg/L. The remarkable selectivity of the method was evaluated by 15 other structurally diverse phenols and anilines. LC-UV and mass spectrometry results corroborated N-1,3-dimethyl butyl-N’-phenyl quinone diamine (6QDI) as the primary oxidation product. Interestingly, we discovered that the protonated form of 6QDI, rather than its neutral counterpart, was the red-colored reaction product with λmax = 490 nm. We further validated the method by applying it to the measurement of 6PPD in a wide array of rubber products and wastes, with 6PPD detected in 22 out of 50 samples. Strong agreement was observed between the colorimetric method and LC-MS measurements, with the highest concentrations detected in car tire rubber. In summary, this study introduces a rapid and cost-effective approach for rapid screening of 6PPD in rubber products and wastes.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
How this classification was reachedexpand
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 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| 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 itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, 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".