## 5 Development of the TF-SPME Technique  
In 2001, [PERSON] and collaborators conceived the first microextraction system, which possessed a solid extraction phase with a higher surface-to-volume ratio than a traditional SPME device. It consisted of a thin film of ethylene-vinyl acetate as the extraction phase, which was applied to glass disks with a diameter of 22 mm [19]. In comparison to 100 \(\upmu\)m SPME fiber, the disk had the following:  
1. More than 1000 times larger surface-area-to-volume ratio of the sorption phase;
2. A smaller volume of the extraction phase. As a result, [PERSON]'s microextraction solution significantly reduced the time the system reached equilibrium but did not increase the sensitivity of the analytical method [9]. In 2003, [PERSON] and colleagues developed a microextraction device that contained a 25.4 \(\upmu\)m thick membrane of prefabricated PDMS as the extraction phase attached to a stainless-steel rod [18]. The sorption process occurred on an unrolled PDMS sheet, which, together with a metal support, resembled a flag (Figure 6). After the sorption was completed, the PDMS membrane was rolled up and placed in the thermal desorption unit of the gas chromatograph. In comparison to SPME microextraction performed with a fiber-coated glass with a 100 \(\upmu\)m PDMS, a 20-fold higher extraction efficiency of polycyclic aromatic hydrocarbons, extracted from an aqueous matrix, was obtained for a 1 cm \(\times\) 1 cm PDMS membrane [18]. Figure 6: [PERSON] TF-SPME system during sorption [18]. In 2006, [PERSON] and co-workers used a 127 \(\upmu\)m thick PDMS sheet in microextraction in a 2 cm \(\times\) 2 cm rectangular shape with an attached 1 cm high triangle hooked to a stainless-steel wire [20] (Figure 7). The applied modification of the shape of the extraction phase determined the increase in its surface area and its volume compared to the rectangular shape used by [PERSON]; so, the sensitivity of the determination of analytes increased. At the same time, the \"house shape\" of the PDMS sheet allowed it to be rolled around a metal carrier and conveniently placed in the thermal desorption unit of a gas chromatograph. In the same year, [PERSON] and his co-workers used for the first time a composite obtained from a combination of polyacrylate and glass wool [21] for the construction of a TF-SPME device. To obtain the microextraction device, they placed the fabric on polyethylene film, which was then saturated with polyacrylate solution and covered with the second sheet of film. After removing the foil layers, they cut the obtained material into strips with dimensions of 6 cm \(\times\) 0.3 cm, adapted to the dimensions of the thermal desorption unit of the chromatograph. The obtained polyacrylate strips were characterized by significantly higher mechanical stability compared to membranes made of pure PDMS. However, after repeated use, they underwent thermal decomposition resulting in reduced mechanical strength and chromatograph deficient [9]. Six years later, [PERSON] and colleagues developed a TF-SPME device with an extraction phase composed of two components: polydimethylsiloxane and divinylbenzene (PDMS/DVB) or carboxene and divinylbenzene (Car/PDMS) [22]. Adsorbent particles (carboxene or DVB) were dispersed in PDMS solution, then applied to a thin sheet of glass wool mesh and spread by spin coating. The resulting material was cut into a \"house shape\"--the rectangle measuring 2 cm per 2 cm--and attached to a 1 cm high triangle, which was then linked to a metal pin. Ultimately, the material was placed in an extraction vessel. After sorption was completed, the active surface was rolled, and thermal desorption was carried out (Figure 8). During the desorption process, the developed sorption material showed significantly higher mechanical and thermal stability compared to [PERSON]'s strips [22]. In 2013, [PERSON] and [PERSON] made a PDMS membrane with applied divinylbenzene with a rod-coating method, which was used for the adsorption and determination of benzene in air [23].