38 May / June 2021 Table 1: Characteristic Pyrolysis Products of the Polymer Standards.
polymers. It degrades into a large number of branched and unsaturated hydrocarbons in the range of C10 to C30.
All pyrograms acquired with the described instrument configuration were compared with accepted literature data [6]. A very good comparability of the data was found.
Table 1 contains the retention indices and the marker ions for characteristic fragments of the different plastics. This database allows us to match markers from reference materials to unknown polymer samples. In the standard ChromaTOF®
software, the features,
‘References’ and ‘Target Analyte Finding’ can be used for this purpose.
In order to identify and semi-quantitate the most used plastic polymers in mixtures or co-polymers, a 3rd party software also was tested. The software tool ChromIdent®
,
(Lablicate GmbH, Hamburg, Germany) [7], applies pattern recognition techniques [8] on pyrolysis data.
ChromIdent® uses a number of
Figure 2: Screenshot of the ChromIdent® analysis with a previously created database.
software showing the results of a comparison of a polymer mix
representative peaks (in this example 150) for each of the nine polymer standards to compile a database. This database then can be used to examine blends or copolymers. The software offers two options: either to compare the peak pattern of the sample against a database or directly against another chromatogram. In this study, a polymer mixture has been compared against the peak patterns stored in the database. In summary, 150 peaks from the sample 10 Mix have been queried against the database Microplastics UK. The most abundant peaks, like toluene, styrene, and 1,3,5-triphenyl- cyclohexane, as well as benzene and 2-methyl-naphthalene, can be used as markers for PS and PVC. Small abundant peaks, like fluorene, should also taken into account. In comparison to other techniques, where a combined mass spectrum of the whole chromatogram or of a few selected peaks is created and used for an identification, ChromIdent®
performs a
deep search on all peaks and the available peak patterns stored in the database. Thus, no prior selection of a few relevant peaks is required, as this is done automatically when compiling the database. Additionally, a retention time shift can be compensated for by using retention indices and the identity mass spectrum as shown in Figure 2. As a result, the plastics PS and PVC can be confirmed as part of the mixture.
Figure 3: 2D Py-GCxGC-TOF-MS contour plot of a pyrolysed filter sample with 12000 features (S/N=25).
To explore the suitability of GCxGC-TOF- MS for analysis of microplastics in complex environmental samples, 2D analyses of the aerosol filter samples were performed. The
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