## 3 Results and Discussion
### Studies on OGN Desorption  
The desorption of unmodified DNA-20 OGN from the three investigated MNPs in two modes was investigated. The influence of the elution solvent pH on the extraction recovery: In the first step of desorption studies in IE mode, the impact of the elution solvent pH on DNA-20 recovery values was studied. The NH\({}_{4}\)OAc salt concentration was 10 mM, while MeOH content was 50% \(v/v\). Other parameters were as described in Section 2.4. Five different pH values were tested: 8.0, 8.5, 9.0, 9.5, and 10.0. The results are plotted in Figure 4a. The pH of the elution solvent has a significant impact on the final recovery. The highest recovery (99.8 \(\pm\) 1.7%) was obtained for MNP-Ac when the pH of the elution solution was equal to 10.0. At pH \(\geq\) 9.0 the desorption of over 90% of DNA-20 was possible (Figure 4a). It was not possible to achieve such high recovery for two other MNP (Figure 4a). In both cases, the highest values of this parameter were obtained at pH = 10.0 and were equal to 77.4 \(\pm\) 4.0% and 86.9 \(\pm\) 2.8%, respectively, for MNP-Sul and MNP-Mal. Independently of which MNP was used, pH dependence on recovery was nearly linear for all MNPs. When pH increase, the values of recovery also increase (Figure 4a). Such an effect relates to the zwitterionic character of MNPs coating. During the adsorption of the OGN, at low pH values, the anionic groups of active ligands are protonated and electrostatic interaction between positively charged imidazolium rings and anionic analytes are possible. When pH increased, gradual deprotonation takes place, and electrostatic repulsion between negatively charged carboxyl or sulfonate groups and OGNs occurs. Thus, a more anionic analyte can be desorbed, and higher recovery values can be obtained. The influence of salt concentration in the elution solvent on the extraction recovery. In the next step, the impact of the NH\({}_{4}\)OAc concentration on DNA-20 recovery values was investigated. The pH of the elution solution was equal to 9.5, the MeOH content was  
Figure 4: The influence of the elution solvent pH (**a**), and salt concentration (**b**), and methanol content (**c**) in the elution solvent on the extraction recovery for MNP-Ac (black bars), MNP-Sul (gray bars), and MNP-Mal (white bars). Experimental conditions in the text. 50% \(v/v\), and other parameters were as in the typical method (Section 2.4). In the studies, five different concentrations of salt were tested: 10, 25, 50, 75, and 100 mM. The results are shown in Figure 4b. The highest amount of OGN was desorbed from MNP-Ac and MNP-Mal using NH\({}_{4}\)OAc in the concentration equaled 100 mM. Obtained recoveries were 99.8 \(\pm\) 2.2% and 88.6 \(\pm\) 5.2% respectively. It is worth highlighting that, for MNP-Ac, the high values (-94%) were also obtained for concentrations 10 and 75 mM (Figure 4b). For MNP-Sul, the highest recovery was obtained for 25 mM concentration of salt in elution solution, and it was equal to 61.6 \(\pm\) 0.6%. For all MNPs in the recovery dependence on NH\({}_{4}\)OAc concentration a similar trend is observed (Figure 4b). At the beginning, with the increase of concentration the recovery values decrease. At some NH\({}_{4}\)OAc concentrations, the desorption efficiency is the lowest. Above this point the recovery increase with an increase in the concentrations. The lowest values for each MNPs are obtained for different salt concentrations. They are 25, 75, and 50 mM for MNP-Ac, MNP-Sul, and MNP-Mal, respectively (Figure 4b). There is a certain analogy of the observed phenomenon to the effect described by [PERSON] for HILIC separations [27]. Probably, different mechanisms characterize interactions in the presence of different salt concentrations. Under the minimum recovery concentration, dissociated salt provides counterions for charged groups bounded to MNPs surface and makes electrostatic interaction of OGN with adsorbent easier. Above this point, desorption efficiency is proportional to salt concentration.