Abstract
The scientific and public interest regarding environmental pollution with plastic particles smaller than 5 mm, also known as microplastic has considerably increased. Nevertheless, the lack of standardized and thoroughly validated operation procedures (for sampling, sample preparation, particle characterization and quantification) currently limits the inter-study comparability of environmental microplastic data sets. On one hand, harmonization of methods can be fostered by development of certified reference materials. On the other hand, time-, cost-efficient and easy-to-use methods are required to integrate microplastic analysis in broad monitoring programs such as existing for legacy pollution. The scientific community frequently uses Infrared and Raman spectroscopy to characterize abundances, polymer types and sizes of microplastic particles in different habitats and biota. Infrared spectroscopy benefits from technical expansions enabling comparably fast microscopy and not being prone to fluorescence, which is a problem for Raman spectroscopy.
A recently introduced alternative to Fourier Transform Infrared (FTIR) spectrometers in conjunction with Focal plane array (FPA) detectors are Quantum-Cascade-Laser (QCL) Systems that emit frequency combs in the infrared range. External cavities enable fast tuning and herewith building up Infrared spectra very fast. Microplastic analysis might benefit from several advantages related with this new technique:
1. Fast imaging with a tailor-made software solution for automated microplastic identification
2. The laser has a ~ 1000 times higher power density than standard globar light sources
3. The detector requires no liquid nitrogen cooling
Nevertheless, first results show that there are still some challenges to master. Especially, when it comes to the analysis of environmental samples bearing a highly complex matrix. To demonstrate the capabilities of the new QCL system it has been applied for the analysis of suspended particlulate matter sample from the German Elbe River estuary, which have been obtained during the testing of two new water-sampling approaches for microplastic. After an iterative optimization process of the spectral library, first results agree with the results obtained by the FPA-based FTIR approach.
