## 6 Methodology for MP Analysis
### Analytical Methods for Identification, Quantification and Characterization of MPs
#### 6.3.3 Chromatographic Methods  
Chromatographic techniques that are most commonly used in MP analysis are thermosetraction desorption gas chromatography with mass spectrometry (TED-GC-MS) and pyrolytic gas chromatography with mass spectrometry (Pyr-GC-MS). Environmental samples are first subjected to thermal decomposition, which involves heating to a temperature of 500-650 \({}^{\circ}\)C in an inert gas atmosphere (TED-GC-MS) or without the presence of oxygen (Pyr-GC-MS) that makes the polymers gradually change from solid to liquid or a vaporous state. Decomposition products are formed, which are first separated on a chromatographic column and then analyzed by mass spectrometry at the molecular level [52; 54; 105]. Identification is carried out based on characteristic ions and their specific ratios, and the quantity is determined from the number of ions released during pyrolysis or thermal desorption of MPs. Some polymers have similar degradation products, so the results can be misinterpreted [53; 105]. Particles smaller than 10 \(\upmu\)m can be qualitatively and quantitatively analyzed [53]. The chemical composition of the entire MP particle is analyzed, which enables identification of individual types of polymers and organic chemicals they interact with (additives and pollutants) [52; 53; 54]. Due to high sensitivity, a small amount of sample is sufficient for the analysis (5-200 \(\upmu\)g). Various physical or chemical effects can change the MP quantity during sampling, pre-treatment and analysis, which affects the quantitative concentration in the sample; therefore, using an MS detector to determine the mass concentration of MPs is more reliable and less susceptible to environmental influences [105].  
TED-GC-MS technique is also appropriate for analyzing significantly larger samples (up to 100 mg), which enables a lower limit of determination, and it is more suitable for the analysis of complex environmental samples and food [41; 52]. No special sample pre-treatment is required, and solid samples can be directly analyzed [105]. However, it has been reported that previous MP extraction or pre-concentration by removing organic and inorganic matter from the sample can improve the performance of the analysis, i.e., increase the reliability of identification and the sensitivity of quantification and, at the same time, reduce background noise and interference [52]. Adding internal standards (e.g., deuterated compounds such as styrene, polystyrene or chlorobenzene) to samples during analysis further improves the quality of the results. It is also recommended to analyze calibration standards and procedural blanks together with the samples for correction of the measured values [52].  
The Pyr-GC-MS method was used for the analysis of model and natural samples of seawater, freshwater, sediment, biota, sewage sludge, air, soil, commercial sea salt and drinking water [52; 105]. The authors constructed a portable device applicable for rapid field analyses of MPs (Pyr-MS) based on MP pyrolysis degradation and mass spectrometry quantification within 5 min.  
Other chromatographic techniques used for MP research are high-temperature gel permeation chromatography (HT-GPC), size-exclusion chromatography with liquid extraction (HDC-SEC) [105] and high-performance liquid chromatography (HPLC) for polymers insoluble in common solvents after the depolymerization process [52].