Quantification of Microplastics by Pyrolysis Coupled with Gas Chromatography and Mass Spectrometry in Sediments: Challenges and Implications

Abstract

Pyrolysis-GC/MS is increasingly used to quantify microplastics (MP) in environmental samples. In general, prior to analysis, purification steps are carried out to reduce the environmental matrix in sediment samples. The conventionally used protocol of density separation followed by digestion of organic matter does not allow for complete isolation of MP from the associated organic and mineral matter. Among the pyrolysis products used as indicator compounds for plastic polymers, some may originate from other substances present in the environmental samples. In this paper, the indicator compounds are reviewed for the most common polymers: PE, PP, PS, PET and PVC and selected taking into account potential interactions with substances present in environmental matrices. Even after a purification step, a residual mineral fraction remains in a sediment sample, including matrix effects. This effect may be positive or negative, depending on the investigated polymer and is thus important to consider when using Pyr-GC/MS for the quantification of MP in sediment samples. It also shows that no external calibration can be used to reliably quantify MP in such samples and that the use of internal standards is compulsory.

Quantification of Poly(vinyl chloride) Microplastics via Pressurized Liquid Extraction and Combustion Ion Chromatography

“…We observed that none of the chlorinated substances and plant components had an interfering effect on the C-IC measurement, and therefore, no influence on the analysis of PVC was observed. Thus, this method is selective for chlorine-containing polymers and is not limited by matrix effects known for other thermoanalytical methods. ,,,,, …”

“…Thus, this method is selective for chlorine-containing polymers and is not limited by matrix effects known for other thermoanalytical methods. 6 , 19 , 24 , 25 , 27 , 28 …”

“…In recent years, different optical analytical methods, such as microscopy, Raman spectroscopy, or Fourier transform infrared spectroscopy, have been used for the identification of various types of plastic particles. − Also, analytical methods using mass spectrometry in environmental samples have been developed for different polymer types, such as polyethylene (PE), polypropylene (PP), polystyrene (PS), poly­(vinyl chloride) (PVC), poly­(ethylene terephthalate) (PET), polycarbonate (PC), or poly­(methylmethacrylate) (PMMA) as well as their additives. − Primarily, pyrolysis or thermogravimetric analysis (TGA) has been coupled with gas chromatograpy/mass spectrometry (GC-MS). − However, these thermoanalytical methods are still under development and suffer from matrix interferences and false-positive results. ,,− For instance, natural compounds from coniferous trees could lead to PE overquantifications . Furthermore, in the case of PS, Fischer et al showed possible overdeterminations by phenylalanine from proteins during pyrolysis-GC-MS .…”

When microplastics meet electroanalysis: future analytical trends for an emerging threat

“…Although some studies reported methods of analysis of MPs using PY-GC/MS without the pre-treatment step (filtration or oxidative processes), the organic matter can still interfere. 114,121 Compared to other thermal analytical methods presented here, Py-GC/MS is the least affected by the organic matter. However, the amount of organic matter contained in the sample will determine if any pre-treatment is needed.…”

“…117–119 However, Py-GC/MS limitations are sample destruction, the inability to detect inorganic additives and suffering from the interference of the residual organic matter and mineral matrix, particularly for sediment samples. 114…”