Evaluation of three pyrolyzer technologies for quantitative pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) of tire tread polymer in an artificial sediment matrix

Transferable and reliable methods for tire and road wear particles (TRWP) environmental mass quantification are needed for environmental risk assessment. The comparative performance of three pyrolysis-gas chromatography-mass spectroscopy (Py-GC-MS) technologies with internal standard was assessed for pure polymers and three cryomilled tire tread (CMTT) samples with or without a standard artificial sediment matrix following ISO Technical Specification (TS) 21396:2017. The pyrolyzer technologies included Curie Point (CP; ferromagnetic induction), microfurnace (MF; ceramic heater), and resistive (R; platinum filament). The dimeric pyrolysis markers for tire tread polymer included: 4-vinylcyclohexene (4-VCH), a marker for styrene-butadiene rubber (SBR) and butadiene rubber (BR); dipentene (DP), a marker for natural rubber (NR) or isoprene; and 4-phenylcyclohexene (4-PCH), a marker specific to SBR not considered in the ISO TS. Comparing the performance of three pyrolysis technologies for quantifying six samples (two tread amount levels for three formulations), the average relative standard deviation in pure-CMTT measured in triplicate using 4-VCH and DP was 6.8% (MF), 26% (CP), and 60% (R) without matrix (100 or 1000 ug CMTT), and 19% (MF), 26% (CP) and 105% (R) with matrix (0.5% or 5% CMTT). The recovery of CMTT was greater than 50% for all MF and CP samples with good separation at the two amount levels. An increased frequency of CMTT recoveries > 150% for MF and CP artificial sediment analysis suggests future consideration of pre-treatment (e.g., thermal desorption or labile organic digestion) in addition to the previously identified importance of polymer microstructure. The magnitude of variability observed with the resistive instrument indicates that further method development may be necessary to optimize thermal transfer. Overall, Curie point and microfurnace were found to be excellent candidate pyrolysis technologies for ongoing quantitative Py-GC-MS of TRWP in environmental method development, capable of a low likelihood of underestimating polymer mass with reasonable replicate precision.