# Preparation of Magnetic Polymers for the Elimination of 3-Isobutyl-2-methoxypyrazine from Wine
## 2 Results and Discussion
### Adsorption Isotherms  
Binding tests were carried out to estimate the adsorption capability of polymers under different initial IBMP concentrations in model wine. The equilibrium isotherms for the adsorption of IBMP onto different imprinted polymers are shown in Figure 4A. The amount of IBMP binding to the polymers increased with increasing initial concentration and no difference was evident among the imprinted polymers according to one-way analysis of variance (ANOVA) and Tukey (HSD) pairwise comparison  
Figure 3: Overlaid Fourier transform-infrared (FTIR) spectra of Fe\({}_{\mathrm{x}}\)O\({}_{\mathrm{y}}\) nanoparticles, Fe\({}_{\mathrm{x}}\)O\({}_{\mathrm{y}}\)@SiO\({}_{2}\), Fe\({}_{\mathrm{x}}\)O\({}_{\mathrm{y}}\)@SiO\({}_{2}\)-MPS, and putative MMIP. Fe\({}_{\mathrm{x}}\)O\({}_{\mathrm{y}}\)@SiO\({}_{2}\): Fe\({}_{\mathrm{x}}\)O\({}_{\mathrm{y}}\) nanoparticles modified with SiO\({}_{2}\); Fe\({}_{\mathrm{x}}\)O\({}_{\mathrm{y}}\)@SiO\({}_{2}\)-MPS: surface-modified magnetic particles; MPS: 3-(trimethoxysily)propyl methacrylate. Figure 2: SEM images of magnetic polymers prepared by conventional thermal synthesis for (**A**) magnetic molecularly imprinted polymer MMIP and (**B**) magnetic non-imprinted polymer (MNIP), and by MW synthesis for (**C**) MW MMIP and (**D**) MW MMIP. (\(p<0.05\)), including those produced with a microwave or with the inclusion of iron oxide nanoparticles. Thus, under the low concentration range used in this study, the different forms of imprinted polymers could not be differentiated from each other. The results of binding tests for thermally synthesised MMIP and MNIPs are shown in Figure 4B, where the adsorption amount also increased in line with the initial IBMP concentrations. The adsorption capability of imprinted polymers was not significantly different from the non-imprinted controls (one-way ANOVA, Tukey (HSD) pairwise comparison, \(p<0.05\)). However, unwashed MMIP had a much lower binding capacity towards IBMP compared to MMIP, which could be due to cavities occupied by the trapped solvent. It was found that the washing process could not only remove template molecules, but also porogen solvent, from the polymers. This highlighted the importance of treating the non-imprinted polymers in exactly the same way as the imprinted polymers to provide proper controls [37]. Several linear and non-linear adsorption isotherm models were applied to fit the equilibrium data of thermally synthesised MMIP and MMIP. Linear models (Table 1) turned out to have a better fit based on their coefficients of determination (\(R^{2}\), Table 2 and Figure S1 of the Supplementary Materials). Polymers were consistently produced using the synthetic procedures outlined in Section 3.2 and batches produced identical results. Both Langmuir and Freundlich isotherms were a good fit for the experimental data. The Langmuir isotherm assumes monolayer adsorption with all sites equivalent to form a homogeneous surface. Once a molecule occupies a binding site, no further adsorption may take place at the same site and a saturation adsorption will be reached, also known as maximum adsorption. On the other hand, the Freundlich isotherm is used to describe surface heterogeneity assuming multilayer adsorption [38]. Though they are based on different theories, both Langmuir and Freundlich models might adequately describe the adsorption at certain concentrations, especially when the concentrations are low and the adsorption capacity of the adsorbent is large enough to make both isotherm equations approach linearity. In the present case, the analytical window is narrow and deliberately limited due to the practical concentration of IBMP in grapes and wines, compared to a concentration range that usually differs by at least two orders-of-magnitude for isotherm determinations. The resultant isotherm may ultimately correspond to only a subset of the sites in MMIP, and while informative, this could be inaccurate and inconsistent for estimating the binding properties in general [39].