## 5 Analytical Techniques for Detection and Quantification of PFAS
### Analytical Detection Techniques  
Mass spectrometry in all of its forms is the elite technique for the identification and quantification of PFAS, and there are numerous examples [141; 142; 143; 144; 145]. [PERSON] et al. [146], aiming to speed up the analysis of PFAS, developed and applied a hyphenated nano-electrospray ionization to HRMS (Nano-ESI-HRMS) to analyze wastewater and aqueous film-forming foams (AFFFs) samples collected from three local wastewatertreatment plants (WWTPs). Nano-ESI-HRMS enables detection of various PFAS with the inclusion of the ultra-short chain and other very polar molecules which are often underestimated in LC. This approach has the advantages of saving time (lower than two minutes per sample) without compromising accuracy and sensitivity. Taking a step forward in the rapid identification of PFAS, [PERSON] et al. [147] devised a quick and efficient method for separating isobar molecules such as 6:2 FTS and Hydro-EVE that differs only for 0.023 m/z. Even with HRMS instruments, mass separation of these precursors is extremely difficult. Collision cross section (CCS) is the phenomenon that underpins ion mobility separation; whereas other LC techniques separate molecules based on their interaction with the stationary phase of the column (polarity) over time, the additional step of this analysis allows for separation based on atom spatial distribution (molecular size). The scientific community is also working to develop new approaches to fight PFAS contamination through various techniques that may be more rapid or \"in situ\". [PERSON] et al. [148] studied albumin as the main protein involved as a carrier for some PFAS compounds in human serum, aiming to use this affinity to rapidly characterize the contaminants. Albumin has numerous nonspecific sites that selectively bind hormones, fatty acids, drugs, and several xenobiotics, particularly PFASs. Prior to the development of the current technology, the methods for determining this affinity, such as surface plasmon resonance or titration chemistry, required too much time because of the large number of distinct PFAS that needed to be examined. Differential Scanning Fluorimetry (DSF) is a quick, high-throughput technique for determining ligand-binding interactions, and it is most frequently used to assess the stability of proteins under various circumstances. The findings showed that DSF can specify protein binding affinities and pinpoint the physicochemical factors that contribute to protein binding for a significant number of PFAS. A different approach to perform a rapid and in situ analysis was found by [PERSON] et al. [149] who discovered the aptamer binding to PFOA (K\({}_{\text{D}}\) = 5.5 uM) phenomenon for the first time, owing to the alkyl length, which is important in the physicochemical event. To investigate this behavior, a fluorescence-based aptasensor was created, which allows for easy and rapid monitoring of PFAS and other emerging pollutants in situ. The results obtained utilizing a multimode plate reader were compared to traditional LC-MS detection methods. NMR spectroscopy and circular dichroism analysis were performed to compare the binding strengths of the aptamer with and without the addition of PFOA, and the results show that the aptamer can bind long alkyl chains with specificity. In parallel to routine quantification of legacy PFAS, in order to monitor the global contamination levels, it is also necessary to detect all possible fluorinated substances, which may be toxic as well. The untargeted approach is the only way to discover all the organic fluorinated compounds, and it is usually performed with high-resolution mass spectrometry [150; 151; 152; 153]. [PERSON] et al. [154] developed for the first time a non-targeted method using fluorine extraction using fluoro-cotton fibers put in SPE cartridges. The interaction F-F aids in the extraction and, as a result, enhancement of organic fluorine compounds.