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Organisationseinheit der BAM
n order to determine the relevance of microplastic particles in various environmental media, comprehensive investigations are needed. However, no analytical method exists for fast identification and quantification. At present, optical spectroscopy methods like IR and RAMAN imaging are used. Due to their time consuming procedures and uncertain extrapolation, reliable monitoring is difficult. For analyzing polymers Py-GC-MS is a standard method. However, due to a limited sample amount of about 0.5 mg it is not suited for analysis of complex sample mixtures like environmental samples. Therefore, we developed a new thermoanalytical method as a first step for identifying microplastics in environmental samples. A sample amount of about 20 mg, which assures the homogeneity of the sample, is subjected to complete thermal decomposition. The specific degradation products of the respective polymer are adsorbed on a solid-phase adsorber and subsequently analyzed by thermal desorption gas chromatography mass spectrometry. For certain identification, the specific degradation products for the respective polymer were selected first. Afterwards real environmental samples from the aquatic (three different rivers) and the terrestrial (bio gas plant) systems were screened for microplastics. Mainly polypropylene (PP), polyethylene (PE) and polystyrene (PS) were identified for the samples from the bio gas plant and PE and PS from the rivers. However, this was only the first step and quantification measurements will follow.
Die Anwendung thermoanalytischer Methoden für die Polymercharakterisierung hat aufgrund der makromolekularen Struktur von Polymere Vorteile. Es wurden zwei neue thermoanalyti-sche Verfahren entwickelt und deren Einsatz anhand von Anendungsbeispielen demons-triert, sowie mit etablierten, thermoanalytischen Methoden verglichen.
Für die thermische- und thermo-oxidative Zersetzungsgasanalytik wurde die Thermogravi-metrie (TGA) gekoppelt mit der Thermodesoptions-Gaschromatographie-Massenspektrometrie (TDS-GC-MS). Die Zersetzungsgase der TGA wurden dafür über ei-nen Festphasenadsorber geleitet, auf dem eine repräsentative Auswahl von polymerspezifi-schen Analyten adsorbiert wurde. Die thermische Extraktion der Analyten erfolgte in der TDS-GC-MS. Dies ermöglichte die Trennung der Analyten sowie die eindeutige Identifizie-rung mittels charakteristischer Massenfragmentmuster. Sie wurde als TED-GC-MS bezeichnet. Es stellte sich heraus, dass sie sich besonders für die Analyse von komplexen Kohlen-wasserstoffgemischen mit Molmassen von mehr als 100 g/mol eignet. In Kombination mit anderen Kopplungstechniken wie beispielsweise die TGA-FTIR/MS, die speziell für die Ana-lyse von kleineren Molekülen verwendet wurde, konnten neue grundlegende Zersetzungs-mechanismen entwickelt werden. Es wurde beispielsweise sichtbar, dass sowohl bei der thermischen als auch bei der thermo-oxidativen Degradation von Polyamid 66 (PA 66) Kon-densationsreaktionen eine wichtige Rolle spielen. Die Methode erwies sich darüber hinaus als besonders geeignet für die Identifizierung und Quantifizierung von Polymeren in Umweltproben. Es entstand dazu eine erste grundlegende Arbeit für die quantitative Bestimmung von Polyethylen (PE) Mikroplastik in Umweltproben.
Im zweiten Teil der Arbeit wurde eine steuerbare beheizbare Zelle eingeführt. Mit ihr war es möglich, mit Hilfe der Nahinfrarotspektroskopie (NIR), sich verändernde Netzwerkstrukturen während der Härtung sichtbar zu machen. Vergleichend dazu wurden etablierte, kalorische Messungen durchgeführt. Somit konnten für verschiedene Epoxidsysteme die Aushärtegrade während der Härtung mit variablen Heizraten bestimmt werden. Dadurch konnten Aushär-tungskinetiken erstellt werden, die durch isotherme und komplexe Aushärtungsszenarien validiert wurden.
Due to the high molecular weights the analysis of polymers is difficult to carry out. Their dissolution is usually limited and the vapor pressure is very low. However, the degradation of a polymer leads usually to smaller compounds which then enable volatile analysis to aid in the characterization of the degradation or decomposition mechanism. The type and the amount of these smaller degradation products is characteristic for the momentary stage of the degradation process.
With thermal desorption coupled to gas chromatography with mass spectrometry (TDS-GC-MS) the polymers can be heated from ambient temperatures to approximately 300 °C. During the heating process small volatile products with a molecular mass up to 350 - 400 m/z were first cryogenic trapping, reheated under controlled conditions and finally separated through a chromatographic column and identified with mass spectrometry. For instance clear differences in the released volatile species of Polypropylene (PP) can be observed depending on the progress of accelerated aging.
In combination with a Thermogravimetric analyzer (TGA) the samples can be heated up to 1000 °C under inert as well oxidative atmosphere. This leads to a complete thermal-pyrolytic or thermo-oxidative degradation of the whole material and a release of degradation fragments over a range of Mw. These fragments enable conclusions for the underlying degradation or decomposition pathways. For coupling to GC-MS a solid-phase adsorption agent can be coupled to the exhaust of the TGA. This adsorption agent is usually a PDMS species that is capable to adsorb compounds with a wide range of polarities. After the thermal extraction the solid-phase adsorption agent will be analyzed by TDS-GC-MS. Therefore, it is possible to determine the species and amounts of the released complex thermal or thermo-oxidative degradation products in detail. This approach offers overall advantageous over existing volatile analytical methods.
Thus, it was possible to determine new thermal and thermo-oxidative degradation mechanism pathways of a well-known material like Polyamide 66 (PA 66). Further example is the unique analysis of small polymer particles, which can be identified and quantified in complex environmental samples. This is our current focus of R&D activities within the framework of the analysis of microplastics in the environment. In the present work we will present a new, automatized set up of this method.
In recent years, an increasing trend towards investigating and monitoring the contamination of the environment by microplastics (MP) (plastic pieces < 5 mm) has been observed worldwide. Nonetheless, a reliable methodology that would facilitate and automate the monitoring of MP is still lacking. With the goal of selecting practical and standardized methods, and considering the challenges in microplastics detection, we present here a critical evaluation of two vibrational spectroscopies, Raman and Fourier transform infrared (FTIR) spectroscopy, and two extraction methods: thermal extraction desorption gas chromatography mass spectrometry (TED-GC-MS) and liquid extraction with subsequent size exclusion chromatography (SEC) using a soil with known contents of PE, PP, PS and PET as reference material. The obtained results were compared in terms of measurement time, technique handling, detection limits and requirements for sample preparation. The results showed that in designing and selecting the right methodology, the scientific question that determines what needs to be understood is significant, and should be considered carefully prior to analysis. Depending on whether the object of interest is quantification of the MP particles in the sample, or merely a quick estimate of sample contamination with plastics, the appropriate method must be selected. To obtain overall information about MP in environmental samples, the combination of several parallel approaches should be considered.
Der Fänger im Spülgas
(2015)