Pyrolysis GC/MS Analysis of Plastic Polymers

Pyrolysis GC/MS measurements
were performed by a multi-shot pyrolyzer
EGA/PY-3030D (Frontier Laboratories, Saikon, Japan) that was attached
to an Agilent 7890A gas chromatograph (Santa Clara, CA) equipped with
an HP-5MS column linked to an Agilent 5975C mass-spectrometer detector.
Pyrolysis was performed according to the parameters used in previous
studies.^{24 (link),39 (link)} Briefly, pyrolysis temperature in single-shot
mode was set at 650 °C for 0.2 min, and the interface temperature
was set at 320 °C. The pyrolysis product was injected with a
split ratio of 50:1. Additional details on the single-shot Py-GC/MS
conditions can be found in Table S3. Mass-based
concentrations were calculated by fitting the obtained results onto
calibration curves.
Seven of the most commonly used plastic
polymers including PVC, PMMA, PP, PS, PE, PET, and PA were analyzed
to determine the characteristic indicator ions (Text S4 and Figure S2).^{24 (link),40 (link)−42 (link)} The selectivity of the indicator ions was tested
by analyzing several selected organic substances including wood, leaf,
fish, humic acid, and black carbon (Table S6 and Figure S6).^{23 (link),41 (link)} Methyl methacrylate (m/z 100), 2,4-dimethyl-1-heptene (m/z 126), 5-hexene-1,3,5-triyltribenzene
(m/z 312), ε-caprolactam (m/z 113), 1,12-tridecadiene (m/z 180), and vinyl benzoate (m/z 148) were selected as indicator ions for PMMA,^{23 (link),24 (link),39 (link)} PP,^{43 (link)} PS,^{23 (link),39 (link),44 (link)} PA,^{45 (link),46 (link)} PE,^{47 (link),48 (link)} and PET,^{41 (link),47 (link)} respectively.
Specific indicator ions for these six polymers were not affected by
tested natural materials (Table S8).^{23 (link),41 (link)} Benzene (m/z 78) shows the highest
peak intensity and sensitivity, while other components have much low
sensitivity; thus, it was commonly selected as an indicator of PVC.^{23 (link),24 (link)} However, natural materials and polymer PS and PET can interfere
with benzene, so PVC was not considered in this study.
External
calibration curves were obtained by analyzing different
amounts of the standard plastics (0.1–10 μg for PMMA,
PA, and PS and 0.1–200 μg for PP, PE, and PET) (Table S4). The identification of a single polymer
in the sample was determined by comparison of the full-scan mass spectra
of specific peaks with the analytical pyrolysis library (Figure S6).^{26 (link)} The
instrument limits of detection and quantification (LOD and LOQ) were
defined as 3 and 10 times the baseline noise, respectively (S/N =
3 and 10).^{45 (link)} LOD and LOQ values were then
converted into procedural limits based on the volume of the original
tested water samples (Table S5).