Microplastic Identification using Micro-FTIR

Chemical identifications of microparticles were done using micro-FTIR. All targeted particles on filters were analyzed using an FTIR microscope (Nicolet iN10; Thermo Fisher Scientific) in transmission mode with the following parameters: 30 μm × 30 μm square field aperture, 8 cm⁻¹ spectral resolution, 64 scans, and 1250–3600 cm⁻¹ spectral range. The obtained FTIR spectra were then compared with the commercial spectral databases of standard polymers (Hummel Polymer sample Library and HR Polymer and additives) and also with open-access libraries designed for microplastic research, which includes spectra of aged plastics^{31 (link)–34 (link)}, using spectroscopy software (OMNIC Picta; Thermo Fisher Scientific). Spectra with a match of < 60% were rejected. When returning a spectral match of > 60%, an additional visual examination of spectra was performed manually, leading to final acceptance or rejection^{35 (link)–37 (link)}. FTIR spectra of typical particles are presented in Fig. 2k–t. Although some anthropogenic cellulosic fibers such as rayon were detected (e.g. Fig. 2j,t), these are not classified as plastics but as celluloses for these analyses.