## 3 Materials and Methods
### Batch Adsorption and Desorption of Polyphenols  
It is well known that surface functional groups regulate the ability of the adsorbents to capture the molecule of interest. Here, the ability of mPEG grafting to bind polyphenols from grape pomace extract was tested. Bare silica particles were used as a control for evaluating the effect of mPEG grafting on polyphenol recovery from grape pomace extract. The batch adsorption experiments were performed in 2 mL centrifuge tubes loaded with 25 mg dry adsorbents. Prior to adsorption experiments, the bare and mPEG silica particles were prewetted with 1 mL of extraction solvent (70:30 (_v/v_) ethanol: water) for 2 h. The particles were centrifuged for 15 min at 15,000\(\times g\) and the supernatant was removed. Then, 1 mL of grape pomace extract (9.1 \(\pm\) 0.3 mg/mL) was loaded to the prewetted particles. The tubes were shaken in an orbital shaker at 125 rpm for 24 h at 25 \({}^{\circ}\)C in dark. After the attainment of adsorption equilibrium, the supernatant was collected and analyzed for total phenolic content. The total phenolic contents of the initial solution and the solution at the equilibrium were measured. The adsorption capacities of the particles were calculated from the difference between the concentrations of initial and final solutions by using Equation (1):  
\[Q_{e}=\frac{(C_{0}-C_{e})\times V_{0}}{m} \tag{1}\]  
where \(Q_{e}\) is equilibrium adsorption capacity (mg/g), \(C_{e}\) is the equilibrium concentration of solute in bulk solution (mg/L), \(C_{0}\) is the initial concentration of solute in bulk solution (mg/L), \(V\) is the volume of the initial sample solution, and \(m\) is the amount of dry adsorbent (g). After acquiring the samples for total phenol analysis, the silica particles were spun and extracts were decanted. Polyphenol-loaded silica particles were washed with 1 mL of extraction solvent (70:30 (_v/v_) ethanol: water). After vortex mixing, the particles were centrifuged for 5 min at 15,000\(\times g\) and the supernatant was discarded. Following this wash step, the particles were resuspended in 1 mL of different elution solvents (200 mM NaCl in 30% ethanol, 200 mM sorbitol in 30% ethanol, 100 mM NaCl and 200 mM sorbitol in 30% ethanol, 200 mM NaCl in 70% ethanol, 200 mM sorbitol in 70% ethanol, 100 mM NaCl and 200 mM sorbitol in 70% ethanol, 10-40% (_v/v_) citric acid in ethanol, 1% HCl in 70% ethanol, 1% NaOH in 70% ethanol, 70% ethanol, 30% ethanol, 10-50% (_v/v_) PEG-400 in ethanol, 10-50% (_v/v_) PEG-400 in water, 50% (_v/v_) PEG-200 in ethanol, 50% (_v/v_) PEG-200 in water) to recover the polyphenols from silica particles. The tubes were shaken in dark at 125 rpm in an orbital shaker. After 24 h, an aliquot of supernatant was collected and analyzed for the total and individual phenolic content. The desorption ratio of the silica particles was estimated using Equation (2):  
\[D=\frac{(C_{d}V_{d})}{(C_{0}-C_{e})V_{0}}\times 100 \tag{2}\]  
where \(D\) is percent desorption ratio, \(C_{d}\) is the concentration of solute in desorption solution (mg L\({}^{-1}\)), \(V_{d}\) is the volume of desorption solution (mL), and \(C_{0}\) and \(V_{0}\) are the same as described in Equation (1) [62]. Developing the Green Solvents for the Recovery of Adsorbed Polyphenols onto the mPEG-Modified Silica Particles  
Since there is strong interaction expected between mPEG ligands and polyphenols, a robust process for the complete recovery of polyphenols is needed. The release of total polyphenols can be facilitated with an elution step. Choosing the right elution solvent for the recovery process is extremely important due to the strict regulations imposed for food and pharmaceutical industry. Therefore, a \"green\" solvent approach has to be implemented for the complete recovery of polyphenols from silica particles. Twenty-one different solvent systems were tested in this study aiming to achieve a complete recovery.