The use of Thermal Desorption Gas Chromatography Mass Spectrometry (TD-GC-MS) to Characterise Plastics, Identify Key Marker Compounds and Differentiate Between Item Types

David Jones¹, Roxana Sühring², Ian D. V. Ingram¹, Ryan Francis³, Laura Miles³, Helen Martin³, Massimo Santoro³, Scott J. Campbell⁴, Scott Coffin⁵, Corey Clutterbuck⁵, Sydney Rilum⁵, Michele Edge¹, David Megson¹

¹ Manchester Metropolitan University, UK. ²Toronto Metropolitan University, Canada. ³Markes International, UK. ⁴SpectralWorks Limited, UK. ⁵California State Water Resource Control Board, USA.

^*The views and opinions expressed in this article are those of the author and do not necessarily reflect the official policy or position of any California State agency.

First presented at BMSS 2023 Manchester, UK. September 2023.

Introduction

Plastic pollution is now an endemic problem in society, and has been identified as a potential planetary boundary threat.1 This project aims to create a standardised method for the sampling and characterisation of plastics using TD-GC-MS. Firstly, unique marker compounds for known plastics and their additives must be found.
Research question: Is it possible to use TD-GC-MS to differentiate by material?

Methods and Quality Control

Samples were macroplastics (plastic items large enough to be handled) all sourced in the USA. The first sample set contained items taken from beaches and the ocean – these are the environmental samples. The second sample set contained store-bought equivalents of those environmental samples.
TD uses gradual heating up to around 300°C to ensure analysis of polymer and its additives rather than degradation products.
The TD analysis method was developed from Markes Application Note 161, which used 1 mg fragments wrapped in quartz fibre filter paper.2 Data analysis performed using SpectralWorks AnalyzerPro® XD.

Results and Discussion

Plot 1. PCA plot of all the store-bought plastic samples. The latex balloons samples cluster away from the others so they have been separated by brand to show that they cluster by sample. The generic brand balloons were made in China. Does the greater chemical consistency of the “USA Factory Certified” balloons correlate with better manufacturing regulations? The TIC for the generic brand balloons is inset.

Plot 2. The latex and PP samples overwhelm the PCA so they were removed to create this plot of mylar vs polystyrene (PS). However, there is no clear clustering in this plot, so we need a volcano plot to find unique chemical components.

Plot 3. Volcano plot for mylar vs polystyrene shows a good number of unique chemical components for both mylar and PS, but also many that exist in both samples. The area graphs (inset) can be used to check for consistent signal in all samples.

Conclusions and Future Work

PCA reveals clustering of plastic items by material
Volcano plots reveal potential unique marker compounds for materials in TD data
Therefore the research question is answered: plastic items can be differentiated by material, and it may also be possible to differentiate by origin
Future work: development of a computational approach to identify which chemical components to examine more closely

Acknowledgements and References

With thanks to the Ocean Conservancy for their work in deciphering beach clean-up data. Additionally, we thank Eva Cicoria and the volunteers at Paddle Out Plastic, Vicki Patterson and the volunteers at Stand Up To Trash, and Richard at the Custodian, for the collection of the environmental plastic samples. This study was partially funded by CIHR, NSERC, and SSHRC through the New Frontiers in Research Fund – Exploration (No. NFRFE-2020-00459).

H. P. H. Arp, D. Kühnel, C. Rummel, M. MacLeod, A. Potthoff, S. Reichelt, E. Rojo-Nieto, M. Schmitt-Jansen, J. Sonnenberg, E. Toorman and A. Jahnke, Environ. Sci. Technol., 55, 7246-7255.
Markes International Application Note 161 is available at markes.com/content-hub/application-notes/application-note-161