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Stability and transformation products of rubber derived compounds under various storage conditions
Summary
A targeted stability study of 23 rubber-derived compounds (RDCs) under varied storage conditions found that methanol at -20°C best preserves sample integrity, while acidified water accelerated degradation, and compounds interact to produce 91 unique transformation products. This is directly relevant to microplastic pollution research because tire rubber is a major environmental microplastic source, and accurately quantifying RDCs in environmental samples requires understanding their transformation chemistry.
Rubber derived compounds (RDCs) are a growing environmental concern. Several chemical classes of RDCs are known for their transformation potential, making the quantification of these compounds in samples difficult if not run directly after sampling. We performed a targeted stability study with 23 standards in a mixture of 31 rubber derived compounds placed under different solvent conditions at three temperature points in order to gauge the long-term stability of the compounds under various storage conditions. Methanol at -20 °C was found to be the best solvent for storage, while acidified DI water was the least stable. Our study indicates that the addition of glutathione at or below 12.3 µg mL-1 does not prevent transformation of PPDs at relevant concentrations. Six compounds that showed loss during the targeted study were investigated using high resolution mass spectrometry to determine what transformations were occurring. Transformations for 2,2,4-trimethyl-2,4-hydroquinoline primarily formed 2,4-dimethylquinoline while 4-ADPA, 4sDPA, and HMMM involved a breakdown of the parent compound. Interestingly, MBT showed negligible loss indicating that the previous degradation was due to inter-compound interactions rather than the solvent they are stored in. Finally, the 31 standard mix was investigated using high resolution mass spectrometry with 91 unique features identified whose formations likely originate from reactions between RDCs. These results showcase the degradation and transformations that can occur for samples awaiting analysis under various storage conditions.