## 4 Methods for Detecting of Microplastic Particles  
The above sections underlined the significance of microplastic pollution. One of the key consequences of this problem is the necessity of determining MP content not only in bottled water but also in other products and environments. Various research teams employ different methods to achieve this goal. A commonly used approach is chemical imaging, which utilizes spectroscopic techniques such as FTIR microscopy (\(\upmu\)-FTIR) and Raman microscopy (\(\upmu\)-Raman) [22; 30; 31; 32]. These techniques provide detailed information on the number, size, and shape of microplastic particles. Additionally, the spectral data collected for each detected particle enable the identification of polymer type. Standardization of research procedures is certainly justified, creating the need to develop a unified method for MP detection. Recently, the European Commission published a decision regarding methods for detecting microplastics in water intended for human consumption [22]. This document provides general guidelines for conducting such analyses. The method outlined in the decision involves several key steps. First, water is filtered through cascade filters, with a minimum sample volume of 1000 L, to collect the MPs. Sample analysis can be performed either directly on the filter or after transferring the sample to an alternative support. To identify the particles, microscopic techniques are used to assess their size, shape, and quantity. In addition, spectroscopic techniques such as Raman microscopy or FTIR microscopy are employed to determine the type of material the particles are made of by comparing the recorded spectrum with a spectral library. The results obtained from these analyses are presented by reporting the number of MPs, expressed as the number of particles per cubic meter of water. The particles are categorized by their shape, size, and material. To simplify the identification process, a pragmatic approach is applied, focusing on 10 priority polymers. The main material of interest in this review, PET, is included in this group of priority polymers. A properly conducted measurement should be verified by assessing the recovery of material through the analysis of a sample with a predetermined amount of MPs. Additionally, the analysis of a blank sample is necessary to determine background contamination. The administrative decision has not yet been implemented, yet it has already faced criticism. Concerns have been raised [31] that due to its restriction to detecting larger particles, the methodology requires refinement. It is designed for the detection of microplastic particles larger than 20 \(\upmu\)m, while the majority of MPs found in bottled and tap water are smaller than 10 \(\upmu\)m [30; 31] (see Figure 4). It is obvious that this topic requires further research and development of better methodology. Therefore, numerous research teams are actively working on this issue. The example of the study [30] shows that there is a great need for guidelines not only to standardize detection methods and develop improved techniques but also to establish harmonized reporting criteria [22]. Defining particle size and shape categories is an undeniable necessity. Moreover, even fundamental aspects, such as data presentation and concentration reporting, require standardization. For instance, MP concentrations can be expressed as the number of particles per cubic meter of water [22] or as mass per volume [31]. Guidelines are also essential to prevent fundamental errors, such as reporting an excessive number of significant digits or presenting numerical values for measurements where the uncertainty far exceeds the measured value [30]. Additionally, the lack of basic statistical analysis further undermines data reliability. When it comes to addressing challenges related to analytical methodology, an interesting and perhaps the simplest approach is to exploit the autofluorescence properties of PET [89].