## 3 Results
### Evaluation of Mesoporous Silicas as Sorbents in SPE
On the other hand, although both EtOH and MeOH are polar solvents, EtOH has a larger molecular structure and can form stronger and more extensive hydrogen bonds and Van der Waals interactions than MeOH [45]. This can facilitate better solvation of the sulfonic groups and the analytes, improving the affinity of the analytes for the material in EtOH compared to MeOH. On the other hand, the differences in performance for these two materials can be explained by considering different factors like the surface characteristics of the sorbents and the num  
Figure 10: Atropine and scopolamine recoveries (% \(\pm\) SD) obtained in SPE assays using 50 mg of MSU-2-SO3H or MCM-41-SO3H as sorbents when the target analytes were loaded in 10 mL of acidified (pH 1) methanol, methanol:water (50:50, \(v/v\)), ethanol or water (0.1 \(\upmu\)g/L of each analyte) and eluted with 3 mL of 5% methanolic ammonia solution. For the remaining conditions, see Figure 2. Error bars represent the standard deviation of replicate samples (\(n=3\)). In each graphic, a different letter indicates a statistically significant difference (\(p\leq 0.05\)). present in them. On one hand, MCM-41-SO\({}_{3}\)H presents a higher degree of functionalization (1.12 mmol ligand/g) than MSU-2-SO\({}_{3}\)H (1.08 mmol ligand/g), which allows for greater interaction with the analytes. However, this higher degree of functionalization is not particularly significant, suggesting that its better performance as sorbent for these analytes is due to its textural properties. These include a larger pore volume (0.69 cm\({}^{3}\)/g vs. 0.52 cm\({}^{3}\)/g) after functionalization, which implies less pore blockage and greater accessibility to bulky analytes like atropine and scopolamine. Additionally, MCM-41-SO\({}_{3}\)H has a more ordered pore structure with greater long-range order, as observed in XRD data, and a more ordered pore distribution, as seen in TEM images. This allows for better and faster diffusion of the analytes throughout the entire volume of the particle, enabling them to reach the active sites of the material where analyte-ligand interactions occur more effectively. To elute the maximum amount of the target alkaloids, it is important to use a desorption solvent that is powerful enough to break the analyte-sorbent ionic interactions while also minimizing the volume of solvent required. Based on our previous works [29] a 5% methanolic ammonia solution was used for this task and the effect of elution solvent volume was evaluated (Figure 11). As can be seen, the increase in the elution volume from 3 to 6 mL of the 5% methanolic ammonia solution did not improve the recovery percentage for atropine. On the other hand, in the case of scopolamine, the increase in the elution volume resulted in a significant improvement with both sorbents when the loading solvent was EtOH (reaching over 95% and 80% for MCM-41-SO\({}_{3}\)H and MSU-2-SO\({}_{3}\)H, respectively), and there were no significant differences when the loading solvent was H\({}_{2}\)O. These results highlight that, in general, the poorer recoveries observed when using MSU-2-SO\({}_{3}\)H as a sorbent compared with MCM-41-SO\({}_{3}\)H are due to lower retention of the analytes in this material and not to a lack of elution, especially when the loading was performed in EtOH. Next, the breakthrough volume was determined. The breakthrough volume in SPE refers to the volume of solvent that can pass through the sorbent before the target analytes start to elute. So, when the breakthrough volume is reached, the analyte begins to appear in the eluate, indicating that the sorbent can no longer retain it effectively.