A Rapid Testing Kit for 6PPD Screening in Rubber Products

<i>N</i>-(1,3-dimethylbutyl)-<i>N'</i>-phenyl-<i>p</i>-phenylenediamine (6PPD) has received increasing attention due to its ubiquitous environmental occurrence and extreme aquatic toxicity of its oxidation product 6PPD-quinone. Given 6PPD's application as an antioxidant in a wide array of rubber products, cost-effective detection of 6PPD is important for product and waste management. We herein developed a rapid testing kit for the detection (<10 min) of 6PPD in rubber products with low costs (<$1/sample), which was inspired by the observation of a red-colored product after 6PPD exposure to oxidants. The selectivity of this reaction was evaluated by 14 structurally diverse phenols and anilines. Interestingly, the protonated <i>N</i>-1,3-dimethyl butyl-<i>N'</i>-phenyl quinone diimine (6QDI+H⁺), rather than its neutral or radical counterparts, appeared to be the red-colored product with λ_max = 490 nm. We further developed a "green" and user-friendly 6PPD rapid testing kit, which was further applied to a wide array of 50 rubber products. 6PPD was detected in 22 out of 50 samples, with a strong agreement (<i>R</i>² = 0.896) observed between the results of the rapid testing kit and LC-MS. In summary, this study introduces a 6PPD rapid testing kit for users without requiring expertise in chemistry.