## 3 Results and Discussion
### Thermal Stability  
Thermal stability determines the operation column temperature range and the lifetime of the GC columns. It is well known that the use of crosslinker agents can affect the thermal stability of PILs-based stationary phases [52]. Thus, the thermal stability of the prepared PILs-based columns was evaluated using two different methods. The first approach was a temperature-programmed GC method that can provide a rough idea of the thermal stability of the PILs-based columns studied [53]. In this case,  
Figure 2: Representation of the efficiency variation of: (**a**) PIL-coated column as a function of the AAIL **4** concentration (noncrosslinked polymers). (**b**) PIL-coated columns with AAIL **4**-DVB as a function of the DVB added (using 0.36% _w/v_ AAIL **4**).  
5-m \(\times\) 0.25 mm fused silica capillaries were coated and subjected to increasing temperatures (from 50 to 400 \({}^{\circ}\)C at 3 \({}^{\circ}\)C min\({}^{-1}\)), and the column bleeding was measured until decomposition was observed. As can be seen in Figure 3, different behaviors were detected. For PILs containing very low crosslinking levels (PIL00 and PIL10), bleeding was observed at temperatures below 250 \({}^{\circ}\)C, which suggests some limitations for their application in GC. On the contrary, PILs with crosslinking degrees \(\geq\) 30% displayed a similar behavior with very good thermal stability and no bleeding below 275 \({}^{\circ}\)C, As a matter of fact, the noncrosslinked PIL column (PIL00) showed the lowest thermal stability (bleeding starting at 225 \({}^{\circ}\)C) and, although not linearly, the incorporation of the crosslinker increased the thermal stability of the PIL-based stationary phases, reaching a maximum for the columns containing a higher degree of DVB (lack of bleeding up to 285 \({}^{\circ}\)C). It must be noted, however, that the efficiency decreases significantly, as mentioned above (see Figure 2b), for crosslinking degrees higher than 20% _w/w_. In this regard, the column based on the polymer PIL20, with 20% DVB, and displaying the higher efficiency, was thermally stable up to ca. 260 \({}^{\circ}\)C, indicating good thermal stability for standard GG applications. This method only gives a rough idea of the thermal stability of the columns studied. Thus, to properly evaluate the thermal stability of the columns, a second alternative set of experiments was carried out using an isothermal method.  
Thus, the second approach was an isothermal method using naphthalene in the 100-350 \({}^{\circ}\)C temperature range. This method is based on holding the GC column at a series of constant temperatures for 12 h and measuring the retention of a well-retained probe compound at a lower temperature, before and after the isothermal conditioning. Table 2 shows the isothermal measurements of naphthalene at different temperatures with the six PIL-GC columns assayed. As can be seen, the retention factor for naphthalene was smaller for the column based on the noncrosslinked linear PIL (PIL00) increasing with the % of DVB for a given temperature. Furthermore, the results confirmed that an increase in the percentage of crosslinker led to an improvement in the thermal stability of the column, with an increase from 230 \({}^{\circ}\)C to 300 \({}^{\circ}\)C for columns with 10% to 60% of DVB, respectively.  
Figure 3: Column bleeding for the PIL-based stationary phases.