## 2 Results and Discussion
### Thermal Characterization of the Poly(Ionic Liquids)  
The thermogravimetric analysis (TGA) plot of the crosslinked poly(methyltetradecyl pyrrolinium) (TFSI) (pD14) film is presented in Figure 2. These experiments allow for accessing the thermal stability of the polymer, while they also mimic the polymer annealing and the fiber conditioning steps. In a first stage, the material was subjected to an increase in temperature to 250 \({}^{\circ}\)C at 10 \({}^{\circ}\)C/min, and then cooled down outside of the oven, allowing for the long alkyl side chains reorganization. Also, some of non-stable polymer fractions, as well as some unknown impurities and solvents trapped in the material, are released, as it can be seen by the weight loss of about 10% during the first 25 min. This step is vital for fiber coating reproducibility. From this point onwards, the material is considered to be prepared and the second stage mimics the fiber conditioning at the GC injector. The objective in the second stage is to evaluate the material thermal stability by placing it at a high temperature (250 \({}^{\circ}\)C) for a long period of time (30 min). As it can be seen in Figure 2, for the pD14 sample, the weight loss is about 1-2% during the whole process, indicating the thermal stability of the materials. The third and final stage of the experiment allows for the determination of the decomposition temperature of the material, which showed an onset temperature of about 355 \({}^{\circ}\)C and 50% of the initial weight loss at 394 \({}^{\circ}\)C. Regarding the other two crosslinked polymers, namely poly(methyloctyl pyrrolinium) TFSI (pD8) and poly(methylethyl pyrrolinium) TFSI (pD2), the results are available the Figures S2 and S3, respectively. In fact, the behavior of these three polymeric materials is very similar. In the first stage, the pD2 loses 9% of weight, while pD8 about 5%. Then, in the second stage, the weight loss is between 0.8% and 1.8% for the three polymeric materials. In the third and final step, the decomposition temperature (\(T_{d}\)) decreases with increasing the alkyl side chain length, from 368 \({}^{\circ}\)C for pD2, 361 \({}^{\circ}\)C for pD8, and 355 \({}^{\circ}\)C for pD14 (Table S1).  
The results of differential scanning calorimetry (DSC) analysis of crosslinked pD14 film are shown in Figure S4. Since pD14 is a crosslinked material, thus an amorphous structure, no melting is expected [30]. However, the presence of glass transition temperature (\(T_{g}\)) is very helpful when developing new materials for SPME since above this temperature the rubbery state is attained, allowing for an easier sorption of the analytes into polymer coating [31]. A \(T_{g}\) can be observed around \(-21\)\({}^{\circ}\)C, confirming the rubbery state of the coating at operation temperatures. The \(T_{g}\)'s observed in the DSC's third temperature cycle of the three materials under study fall in the same region, between \(-16\)\({}^{\circ}\)C and \(-23\)\({}^{\circ}\)C (Table S1 and Figure S5), thus rendering a large range of working temperatures for these coatings, both in the sorption and desorption steps.  
Figure 2: TGA thermogram of crosslinked poly(methyltetradecyl pyrrolinium) (TFSI) (pD14).