## 5 Analytical Techniques for Detection and Quantification of PFAS
### Sampling and Storage  
The first step to improve the level of detection and quantification in complex matrices, in particular from the environment (air, water, soil), is the sampling. For analyzing 26 PFASs in drinking water treatment plant (DWTP) [PERSON] et al. [129] used two approaches, based on hydrophilic-lipophilic balance (HLB) and weak anion exchange (WAX) of polar organic chemical integrative samplers (POCIS) which were calibrated and used in the investigation. The average PFAS concentration was measured to be rather stable over the course of the days, demonstrating the suitability of the calibration method used for the passive samplers POCIS-WAX and POCIS-HLB. In general, there were no appreciable differences in the detection of individual PFAS contents in drinking water between POCIS-WAX, POCIS-HLB, and composite water samples (collected in aliquots during periods). It is noteworthy that POCIS-HLB had low absorption rates, which may account for the fact that perfluorobutanoic acid (PFBA) was only found using POCIS-WAX and composite water sampling. New microporous polyethylene (PE) diffusion passive sampler was also tested for PFAS groundwater monitoring [130]. Using this design, the linear absorption phase of PFASs was successfully extended and a mean t\({}_{1/2}\) of 240 days was estimated.  
For testing the best condition for storing the samples, [PERSON] et al. [131] measured the stability of 29 PFAS in different types of water stored at different temperatures. PFAS were spiked in different water samples that were then kept in HDPE containers for up to 180 days at +20, +4, and \(-20\)\({}^{\circ}\)C. The study showed that keeping the samples below 0 \({}^{\circ}\)C is the only way to ensure the stability of PFAS over time because the effects of the analyte interconversions were noticeable within 7 days of storage at 4 \({}^{\circ}\)C, which is the temperature that is normally used to stock aqueous samples for analysis of PFAS.  
In case of air samples, to overcome the issue of sampling air including the particulate matter and the gaseous phase for the discovery of unknown novel PFASs, the study of [PERSON] et al. [132] showed the use of a cryogenic air sampler (CAS) to simultaneously collect atmospheric gaseous phase and particulate matter comprehensively. Five groups of chlorinated perfluoropolyethers were reported for the first time in this study.  
[PERSON] et al. [133] studied a fast and simple extraction method for PFAS contaminated soil. The samples of soil were freeze-dried or air-dried before analysis and were also  
\begin{table}
\begin{tabular}{l l l l l} \hline \hline  & **Sampling and Storage** & \multicolumn{2}{c}{**Extraction and Clean-Up**} & \multicolumn{2}{c}{**Analytical Detection Techniques**} \\ \hline  & - & QuEChERS & - & 2D-LC-HRMS \\ - & POCIS (WAX, HLB) & - & C18 & - & LC-MS/MS \\ - & microporous PE diffusion & - & Z-Sep & - & LC-HRMS \\  & passive sampler & - & EMR-lipid & - & ICP-MS \\ - & CAS & - & dSPE & - & FT-LC-MS \\ - & Different depth levels & - & ITSP & - & NMR \\ - & HDPE containers at different T & - & Multistep sorption and filtration & - & GC-MS \\ - & Freeze or air-dry & - & with cellulose & - & DSF \\  & - & ultra-centrifugation & - & Aptasensor “in situ” \\  & - & SPE (WAX or F-cotton fibers) & - & Circular dichroism \\ \hline \hline \end{tabular}
\end{table}
Table 6: Scheme of analytical techniques strategy.  
collected from different locations. [PERSON] [134] analyzed soils samples collected at different depth levels. It was the first known study of this type and the results showed that this sort of sampling provides insightful information about the type, source and the consequence of the contamination.