Manual analysis:

FPA-µFT-IR-Imaging spectroscopy for MP analysis:

First example of automatic pipeline (AWI)

Marking

particles as MP

For detecting the microplastics in the sample, an automated algorithm is applied where all reference spectra in the database are compared to all spectra in the map. The reference database contains both plastic polymers and natural materials, having spectra that show similarities to those of the plastics, have been used. The various materials in the spectra-database are assigned to different material groups such as PP, PE, PET, and so on. The algorithm used for detecting microplastic particles applies 2 thresholds of probability score. First the algorithm finds all pixels where the highest probability score  belongs to a plastic material and where that score is above the higher threshold. It analyses all the adjacent pixels and adds them to the plastic particle if they have a material belonging to the same material group and which has a probability score above the second threshold.

Measuring

dimensions

The so-identified plastic particles are then analyzed for the longest distance between pixels of the particle, yielding the major dimension of the particle. The minor dimension is found by assuming the particle shape is an ellipse and knowing the area of the particle in the scan. The third dimension, the thickness, is assumed as being 0.67 times the minor dimension. The volume is calculated assuming the particle is an ellipsoid. The mass is calculated from the volume and the density of the identified plastic material.

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