Previous successes and untapped potential of pyrolysis-GC/MS for the analysis of polluted plastics
Meredith Seeley, Jennifer Lynch
There is growing concern from scientists, policy makers and the public about the pollution of natural and indoor environments with plastic, particularly micro/nanoplastics. Typically, characterizing this pollutant is achieved with extensive sample processing to isolate particles, followed by spectroscopic methodologies to identify particle polymer composition. In most cases, this cannot provide polymer mass or advanced chemical composition (e.g., chemical additive content), which are increasingly requested for toxicological assessments. To achieve mass fraction quantification of polymers in, and advanced chemical characterization of, environmental samples, many researchers have turned to advanced thermoanalytical spectrometric approaches, particularly pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). Despite its growing popularity, there are a variety of approaches to Py-GC/MS attributable to the various thermal program possibilities and sample/calibrant preparations. While single-shot or 'flash' pyrolysis (i.e., instantaneous heating at a single temperature >500 °C) has been most commonly utilized, a double-shot approach (which first thermally desorbs a sample from 100 °C to 300 °C followed by flash pyrolysis) has value to both identify additives as well as remove interference from natural matrices. Even less commonly used approaches, including evolved gas analysis and thermal slicing are also introduced here for their advantages and disadvantages. Following pyrolysis, a series of specific marker pyrolyzates (i.e., degradation compounds of polymers under pyrolysis temperatures) are used to confirm the polymer or co-polymer identity. Great strides have been made in using calibration curves of a marker or markers to quantify plastics in complex matrices. These calibrations are not without challenges, however. The simplest approach for building calibration curves for Py-GC/MS data is weighing calibrant polymers; however, the lower limit of calibration is often constricted by the analytical balance precision. An improved limit of detection can be achieved by using pressurized solvent extraction approaches, but solubility varies between polymers/solvents and polymers have the propensity to precipitate, requiring careful evaluations. Sample preparation may also be approached similarly to preparation needed for spectroscopic approaches (i.e., isolate particles on a solid matrix, for example, a filter). Notably, the use of internal standards has improved polymer quantification, but recent work reveals potential matrix interference issues. Moreover, novel preparation approaches can also facilitate analysis of nanoplastics specifically, which is sorely needed in the field. In all, this summary of previous work is used to highlight opportunities for improved and harmonized Py-GC/MS analysis of polluted plastics. These recommendations include: (1) process samples and calibrants identically within each sample set, (2) where possible, size-sort the particles from a samples prior to analysis to improve polymer-size estimates, (3) use internal standards, preferably carbon-labeled polymers, for quantification, (4) use double-shot pyrolysis to qualify and quantify additives and reduce matrix interference, (5) support and use open-access platforms to facilitate Py-GC/MS data sharing between users, improving sample polymer and additive identification, (6) preserve data for future analysis by using scanning ion methods, and (7) use unique approaches to qualify environmental weathering.
and Lynch, J.
Previous successes and untapped potential of pyrolysis-GC/MS for the analysis of polluted plastics, Analytical and Bioanalytical Chemistry, [online], https://doi.org/10.1007/s00216-023-04671-1, https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=936129
(Accessed March 2, 2024)