## 6 Methodology for MP Analysis
### Analytical Methods for Identification, Quantification and Characterization of MPs
#### 6.3.2 Spectroscopic Methods  
MPs are typically a heterogeneous mixture of plastic particles of varied and complex compositions, and the analysis of their chemical composition is based on the determination of functional groups, molecular weight, structure and the degree of polymerization [105]. For the representative analysis of MPs, vibration spectroscopic methods (FTIR and Raman) are most often used. These are based on the interaction of radiation and molecular vibrations and can identify the type of polymer, quantify their number and determine the shape, size and distribution of the particles [53]. The recorded spectra of the samples are compared to the reference spectrum from the literature database [54; 105]. Commercial spectral libraries usually contain the spectra of original intact synthetic polymers, which can differ significantly in practical application due to the presence of additives and MP changes in the environment. Therefore, some open-access spectral libraries are established that are supplemented with practical examples of MP spectra found in nature (e.g., SLoPP, SLoPP-E, RDWP and Open Spec) [52]. Fourier transform infrared spectroscopy (FT-IR) enables the accurate identification of polymer type based on the measurement of its IR spectrum [54; 105]. The analysis provides information on the amount of MP particles and their structure (chemical bonds and functional groups) and enables the assessment of degradation or weathering of the material. The sample must be previously cleaned of other impurities and completely dry because moisture interferes with the analysis, which is the main limitation of the method [52]. The preliminary preparation procedure and measurement device settings should be adapted to the sample type being analyzed since the particle size, color and shape of MPs affect the analysis [53; 105]. Each particle in the sample is analyzed separately, which is time consuming. Dark and opaque materials and irregular particles smaller than 20 \(\upmu\)m are difficult to analyze [14; 105]. The combination with an optical microscope (\(\upmu\)-FTIR) improves the efficiency of identification [105] and enables the analysis of particles up to 5 \(\upmu\)m in size [53]. \(\upmu\)-FTIR analysis can be performed on individual manually isolated particles or their optical images as well as simultaneously on the entire filtered area [52]. In some MP studies, a similar technique of NIR spectroscopy was used for measurements at wavelengths close to the IR spectrum [41; 103]. This could be used as a screening method before more detailed spectroscopic analyses [52]. Studies also report the application of FTIR with attenuated total reflection (FTIR-ATR) for the description of MP composition [52; 54; 101; 106] and FTIR with FPA detector (focal plane array-based reflectance) and its improved automated version FPA detector-based \(\upmu\)-FTIR imaging [52; 105], for which a free software tool for the systematic identification of MPs in the environment (siMPle) was developed [52]. Raman spectroscopy determines the presence and type of MPs in samples based on the scattered light reflected by the sample molecules when they are in an excited state [53]. Different structures of different molecules and atoms have different frequencies of scattered light due to vibrations induced by changes in the polarization of chemical bonds, which results in the Raman spectrum [105]. The resolution of the Raman spectrum enables the analysis of particles up to 1 \(\upmu\)m in size [14; 105]. A small amount of sample is sufficient for the analysis. The samples do not have to be dried and dehydrated, but they must be completely cleaned of organic matter [53]. The main method limitation is the interference of fluorescent components naturally present in the environmental sample (e.g., clay minerals, dust, hummus, microbiological and biological impurities [52]) or formed during the pre-treatment process (e.g., iron residues after digestion with [PERSON]'s reagent [57]).