Platinum atr unit

For identification of plastic items from surface sampling, a subset of 38.4% (total: 1075) of all items from field LK and 100% (total: 314) of items from field HB were analysed with a with a Tensor 37 FTIR spectrometer (BrukerOptics GmbH) combined with a Platinum-ATR-unit (BrukerOptics GmbH). Each item was measured after 16 background scans by 16 sample scans (spectral resolution: 4 cm⁻¹ in a wavenumber range of 4000–400 cm⁻¹). Spectra identification was carried out with the internal OPUS 7.0 (BrukerOptics GmbH) database, showing average OPUS-HIT ratios of 619.3 (LK) and 601.9 (HB). For microplastics from soil samples, a subset of 35.4% (total: 99) particles was analysed with a µFTIR spectrometer (Lumos II, BrukerOptics GmbH) with 30 background and 30 sample scans (spectral resolution: 4 cm⁻¹ in a wavenumber range of 4000–680 cm⁻¹). µFTIR spectra were identified using spectra correlation via OpenSpecy^{59 (link)}, resulting in an average r² of 0.84. Each plastic item or microplastic particle, regardless of the spectrometric analysis, was classified according to its visual surface characteristics (particle type, surface form and surface degradation)^{60 (link)}. Statistical operations were performed in Microsoft Excel 2021 (Microsoft), and R (R Core Team, 2020), using RStudio (Version 3.4.1; RStudio Inc.). Spatial data analysis and processing was performed in QGIS⁶¹ .

For identification and quantification, all potential plastic particles were analysed with a Tensor 27 FTIR spectrometer (Bruker Optik GmbH) further equipped with a Platinum-ATR-unit (Bruker Optik GmbH). For the measurement of each particle, 16 background scans were pooled, followed by 16 sample scans with a spectral resolution of 8 cm⁻¹ in a wavenumber range from 4000 cm⁻¹ to 400 cm⁻¹. Obtained spectra were analysed with the software OPUS 7.5 (Bruker Optik GmbH) through comparison with polymer reference spectra from a custom-made database containing the most common polymers as well as natural materials^{47 (link)}. Besides polymer type, colour and shape of each particle were recorded. Measurements of macroplastic area and length measurements for micro- and macroplastic were conducted with the image processing program ImageJ (version 1.51j8). If macroplastic pieces exhibited holes, those areas were subtracted from the total area. As the width of the size classes for particle size distribution analyses were not uniform, the particle numbers were normalized by dividing the total particle numbers of each size class by the width of the size class (in mm). Finally, to obtain the dry weight of the particles, each particle was carefully cleaned under de-ionized water and dried (at 40 °C) until stable weight, which was obtained with a precision scales (Ohaus Explorer EX225D/AD ± 0.1 mg).

The method of IR spectroscopy was used to study intermolecular interactions and control the completeness of substitution of protons by sodium ions and the absence of water in the membrane samples. ATR IR spectra of the prepared samples were recorded under vacuum (<1 hPa) on spectrometer Vertex 70V (Bruker Corporation, Karlsruhe, Germany) at room temperature using a Bruker diamond attachment for the range 50–4500 cm⁻¹ (resolution 4 cm⁻¹, 16 scans). The spectra were registered with a single bounce Platinum ATR unit (Bruker Corporation, Karlsruhe, Germany) with Diamond crystal. At this scale, the spectra are normalized by the fixed depth of light penetration into the sample, thus ATR spectra in the distant IR region up to 50 cm⁻¹ inclusive may be studied. Time of operation at which the hygroscopic sample was in the air along with the time required to transfer the sample into the attachment prior to start of evacuation of the cell holder of spectrometer was not more than 0.5 min.