## 7 Sorbents Used in the TFME Technique  
The variety of physicochemical properties of analytes in samples with complex matrices such as food, biological, and environmental samples requires the use of extraction phases in the TF-SPME technique, which are characterized by sufficient high sensitivity, selectivity, sorption capacity, and mechanical, thermal, and chemical resistance [15]. The K\({}_{\text{eq}}\) partition constant of the sorption surface and the analyte extracted from a given matrix directly impact its microextraction process's selectivity, efficiency, and speed. The value \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Technique**} & \multirow{2}{*}{
\begin{tabular}{c} **Film Thickness** \\ **Achieved** \\ \end{tabular} } & \multirow{2}{*}{**Advantages**} & \multirow{2}{*}{**Disadvantages**} \\ \hline Dip coating & & & \(\bullet\) & High homogeneity and mechanical stability & \(\bullet\) & Difficult to coat \\  & Low \(\upmu\)m range & & of a layer & & flexible substrates \\  & Low & \(\bullet\) & Simple process and setup & \(\bullet\) & Large amount of \\  & & \(\bullet\) & Low cost & & solution wastage. \\ \hline \multirow{5}{*}{Spin coating} & & & \(\bullet\) & High mechanical stability of a layer & \\  & & & \(\bullet\) & A simple and effective process that requires & \\  & & & minimal training to master & \(\bullet\) & Variation in the thickness \\  & & & &  between the central part and \\  & & & \(\bullet\) & Cost-effective & \\  & & & \(\bullet\) & No requirement for any high-energy & \\  & & & & & \\  & & & & processes & \\  & & & \(\bullet\) & Possibility to produce TF-SPME extractive & \(\bullet\) & High level of solution waste \\  & & & & phase with or without a supportive core & \\ \hline \multirow{5}{*}{Electrospinning coating} & & & \(\bullet\) & High homogeneity and mechanical stability & \(\bullet\) & Sensitivity to the manufacturing \\  & & & \(\bullet\) & Possibility to produce TF-SPME extractive & & environment (temperature \\  & & & & phase without a supportive core & \(\bullet\) & Slow process rate \\ \hline \multirow{5}{*}{Bar coating} & & & \(\bullet\) & Possibility to produce TF-SPME extractive & & \\  & & & phase with or without a supportive core & & \\  & & & \(\bullet\) & Possibility to prepare uniform films on & \\  & & & rigid or flexible substrates & & \\  & & & & & rod structure and \\  & & & & High homogeneity and mechanical stability & \\  & & & of a layer & & \\  & & & & & \\  & & & \(\bullet\) & Simplicity to change the coating thickness & \\  & & & \(\bullet\) & Simple and quick process & \\  & & & \(\bullet\) & Low cost & \\ \hline \multirow{5}{*}{Spray coating} & & & \(\bullet\) & Simple process & \\  & & & \(\bullet\) & High mechanical stability of a layer & \(\bullet\) & Poor homogeneity of the layer \\ \cline{1-1}  & & & \(\bullet\) & Low cost & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Techniques used for preparation of TF-SPME devices. Figure 14: Schematic diagram of the spray-coating method [29]. of the partition constant is determined mainly by the chemical and physical structure of the extraction medium used in the TF-SPME device. The selection of the material constituting the extraction phase is, therefore, a key factor affecting the method's sensitivity for determining the analyte [30]. Polar solvents have an affinity to hydrophilic compounds whose molecules contain polar functional groups such as hydroxyl, amine, and carboxyl. A principal feature of non-polar sorbents is a high affinity to hydrophobic organic compounds whose molecules are mainly composed of non-polar hydrocarbon chains or rings. The achievements of recent years in the field of materials chemistry have contributed to the use of the most diverse classes of materials in microextraction techniques. The materials show features such as high specific surface area, good wettability and ease of their chemical modification, and the presence of suitable functional groups that enhance interactions with the analyte [31].