Microplastic: New method for the analysis of water samples

Raman microscope

In recent years, research in the field of microplastic analysis has increased greatly. Microplastics (synthetic polymer particles with diameters of 1 μm to 5 mm) have been discovered in various environmental matrices like biota, sediments, surface waters and seawater as well as in food and mineral water. Due to missing standardization of sampling, sample preparation and analysis methods (e.g. pyrolysis gas chromatography mass spectrometry, micro-Fourier-transform infrared spectroscopy (μ-FTIR) and Raman-microspectroscopy (μ-Raman), research results are in many cases not comparable and often not resilient.

A method developed at TZW: DVGW-Technologiezentrum Wasser (German Water Centre) has been validated and is based on a fractionated filtration unit. This filtration unit consists of three brass filter cartridges, each equipped with a stainless steel filter mesh with various mesh sizes (100 μm, 20 μm, and 5 μm). It is suited to sample surface water as well as processed drinking water with a sample volume between 0.3 m³ and 14 m³. During the sampling procedure, particles are enriched on the stainless steel filters and can afterwards be extracted from the filter meshes using ultrasonic extraction. The extracts for drinking water samples are directly filtered over PTFE filter membranes and analysed, while surface water extracts require a clean-up before final filtration. Samples are analysed by confocal μ-Raman microscopes. At least 20 - 50 % of the filter area is measured and the obtained spectra are semi-automatic compared with databases for particle identification.

The analysis procedure was validated by a recovery test with reference microplastics of different polymer types and sizes. The validation of the method, including sampling, sample preparation and analysis yielded an average overall recovery of 81%. As quality control a process blank is analysed regularly. Currently TZW is developing a supplementary μ-FTIR analytical method.

Link to project details MiWa