The measurements were conducted using a µ-Raman spectroscope (DXR2xi, Thermo Fisher Scientific Inc., Waltham, MA, USA) with a front-illuminated EMCCD detector. For measurements, the electron multiplier (EM) was turned off. All particles from 20 to 140 µm (PP samples) or > 50 µm (PVC samples) on the filter were detected using the automatic particle recognition feature of the instrumental software OMNICxi (v.2.3, Thermo Fisher Scientific Inc., Waltham, MA, USA). Each detected particle was analyzed with a laser wavelength of 785 nm, a laser power of 8 mW, and a total exposure time of 6.75 s (three repetitions of 2.25 s each). The objective used had a 20 × magnification and a numerical aperture of 0.45. Spectra were recorded in the range of 50–3300 cm−1 and with a resolution of 5 cm−1.
The spectra recorded were compared with the reference library P/N L60001 (S.T. Japan Europe GmbH, Köln, Germany) using OMNICxi and OMNIC (v 9.11.706, Thermo Fisher Scientific Inc., Waltham, MA, USA). Due to a large number of false positive and false negative results, all spectra were manually checked by a researcher. The particle size was determined automatically by OMNICxi based on the greatest particle diameter. Since the dosed MPPs were white or transparent, no colored MPPs were included. In addition, no MP fibers were included.
The spectra recorded were compared with the reference library P/N L60001 (S.T. Japan Europe GmbH, Köln, Germany) using OMNICxi and OMNIC (v 9.11.706, Thermo Fisher Scientific Inc., Waltham, MA, USA). Due to a large number of false positive and false negative results, all spectra were manually checked by a researcher. The particle size was determined automatically by OMNICxi based on the greatest particle diameter. Since the dosed MPPs were white or transparent, no colored MPPs were included. In addition, no MP fibers were included.