Lecture
Quantification of microplastics in complex environmental samples: A real polymer nut to crack
- at -
- ICM Saal 3
- Type: Lecture
Lecture description
G. Dierkes, Koblenz/DE, T. A. Ternes, Koblenz/DE
The determination of microplastic mass concentrations, which consists of synthetic polymers, requires the employment of specialised analytical methodologies, a consequence of their low solubility, elevated molecular weights and minimal vapor
pressure. In many cases, it is necessary for polymer chains to be degraded into smaller molecules prior to analysis. The process may be accomplished through the utilisation of elevated temperatures, a method known as pyrolysis, or through a chemical approach involving solvolysis [1]. It is therefore impossible to quantify synthetic polymers directly; instead, this must be achieved indirectly through the use of specific marker compounds. Consequently, the analytical results do not represent a specific molecular species, but rather a sum parameter for all compounds forming the marker compound during analysis. The judicious selection of these marker compounds is imperative to ensure the accurate and reliable quantification, even in complex matrices.
A common approach for the quantification of synthetic polymers in environmental samples is the use of pyrolysis gas chromatography/mass spectrometry (py-GC/MS). The degradation of polymers into volatile molecules is conducted at temperatures of
approximately 600°C, and the analysis of these via GC/MS. For quantification, it is crucial that the marker compounds used for quantification are not formed from the sample matrix, and that their formation rates are independent of it. In a multitude of instances, these criteria are not met. Marker compounds for polyethylene (PE), a series of homolog alkenes and alkadienes, or polyvinyl chloride, e.g. methyl naphthalene, are also released from natural organic matter (NOM), resulting in overestimations. Conversely, the presence of inorganic matrix compounds such as ferrous minerals has been observed to impede the pyrolysis process, resulting in signal suppression [2]. Therefore, separation of the matrix prior to py-GC/MS analysis is mandatory. One opportunity is the extraction of the polymers by organic solvents at elevated temperatures [3]. Nevertheless, this methodology is confined to extractable polymers, which excludes crosslinked polymers
such as rubbers. In conclusion, the quantification of synthetic polymers in complex environmental samples is a highly challenging task. Given the extensive range of polymers, a universally applicable method is not yet available; rather, a number of specific methods are required to capture the full spectrum of microplastic pollution.
Literature:
[1] G. Dierkes, The Handbook of Environmental Chemistry 2021, vol 111.
[2] T. Lauschke, J. Anal. and Applied Pyrolysis 2023, Volume 174: 106108
[3] G. Dierkes, Anal. and Bioanal. Chem. 2019, 411:6959-6968
The determination of microplastic mass concentrations, which consists of synthetic polymers, requires the employment of specialised analytical methodologies, a consequence of their low solubility, elevated molecular weights and minimal vapor
pressure. In many cases, it is necessary for polymer chains to be degraded into smaller molecules prior to analysis. The process may be accomplished through the utilisation of elevated temperatures, a method known as pyrolysis, or through a chemical approach involving solvolysis [1]. It is therefore impossible to quantify synthetic polymers directly; instead, this must be achieved indirectly through the use of specific marker compounds. Consequently, the analytical results do not represent a specific molecular species, but rather a sum parameter for all compounds forming the marker compound during analysis. The judicious selection of these marker compounds is imperative to ensure the accurate and reliable quantification, even in complex matrices.
A common approach for the quantification of synthetic polymers in environmental samples is the use of pyrolysis gas chromatography/mass spectrometry (py-GC/MS). The degradation of polymers into volatile molecules is conducted at temperatures of
approximately 600°C, and the analysis of these via GC/MS. For quantification, it is crucial that the marker compounds used for quantification are not formed from the sample matrix, and that their formation rates are independent of it. In a multitude of instances, these criteria are not met. Marker compounds for polyethylene (PE), a series of homolog alkenes and alkadienes, or polyvinyl chloride, e.g. methyl naphthalene, are also released from natural organic matter (NOM), resulting in overestimations. Conversely, the presence of inorganic matrix compounds such as ferrous minerals has been observed to impede the pyrolysis process, resulting in signal suppression [2]. Therefore, separation of the matrix prior to py-GC/MS analysis is mandatory. One opportunity is the extraction of the polymers by organic solvents at elevated temperatures [3]. Nevertheless, this methodology is confined to extractable polymers, which excludes crosslinked polymers
such as rubbers. In conclusion, the quantification of synthetic polymers in complex environmental samples is a highly challenging task. Given the extensive range of polymers, a universally applicable method is not yet available; rather, a number of specific methods are required to capture the full spectrum of microplastic pollution.
Literature:
[1] G. Dierkes, The Handbook of Environmental Chemistry 2021, vol 111.
[2] T. Lauschke, J. Anal. and Applied Pyrolysis 2023, Volume 174: 106108
[3] G. Dierkes, Anal. and Bioanal. Chem. 2019, 411:6959-6968
