## 1 Introduction  
Grapes, with annual production of more than 77 million tons, is one of the largest fruit crops in the world [1]. Winemaking utilizes almost fifty percent of worldwide grape production [1]. However, large quantities of byproducts such as pulp, seeds, and skins remain unused in the process. These byproducts, so-called grape pomace, are a good and cheap source of high-quality natural polyphenic compounds [2]. The economic implications of polyphenols are thought to be substantial because of their potential applications in cosmetic and pharmaceutical formulations in addition to the food processing industry [3]. In recent years, polyphenols have gained significant attention due to their important role in preventing obesity, coronary heart disease, colon cancer, gastrointestinal disorders, and reducing the risk of diabetes [4; 5]. It was also shown that these compounds can be utilized for topical antiaging purposes [6]. Several unit operations are currently available for the isolation of polyphenols from complex plant matrices. Solid-liquid, supercritical fluid, accelerated solvent, ultrasound-assisted, microwave-assisted, subcritical water, and enzymatic-assisted extractions are among some of the extraction methods reported in the literature [7]. However, due to the cost constraints of other techniques, solid-liquid extraction is the most commonly used method for the isolation of polyphenols from grape pomace [7]. The process, however, is not selective for polyphenols and does not meet the purity demands of the pharmaceutical industry. Therefore, a purification step is essential for the recovery of polyphenols from grape pomace extract. Polymeric resins such as polystyrene-divinyl benzene co-polymeric resins (PS-DVB) are widely used to separate phenolic compounds from crude plant extracts due to their high surface area and correlating high adsorption capacities [8]. The separation mechanism of these resins is based on hydrophobic interactions and van der Waals forces and these interactions are known to be nonspecific [9; 10]. Nonpolar polymeric resins show low selectivity towards polyphenols and form weak interactions to polar compounds such as polyphenols [11; 12]. These drawbacks limit the purity of polyphenols recovered from grape pomace extract using nonpolar resins if no secondary purification method is used [12; 13; 14]. A few attempts using resins capable of forming hydrogen bonds improved the selectivity towards polyphenols, however, they suffer from low adsorption capacity [15; 16]. Polyphenols consist of several hydroxyl and carboxyl groups and the number and position of these groups vary among the polyphenol families [17]. It is likely that the orientation of the groups will determine their affinity to polar functional groups on the adsorbents. Therefore, adsorbents grafted with tunable ligands are needed for targeted separation of individual or subgroups of polyphenols [15]. However, polymeric resins cannot provide tunable surface properties and it is tedious to prepare them with the desired surface properties. In this work, we developed a purification method for the recovery of polyphenolic compounds using silica particles grafted with polyethylene glycol (PEG) ligands. Silica is widely used in the delivery of therapeutics and chromatography due to its robust nature with well-known aqueous based synthesis protocols and modularity [18; 19]. Silica particles can be functionalized with a variety of silanes to introduce hydrophobic, charged, or polar moieties to their surfaces [20; 21]. Therefore, silica was chosen as a support for the target ligand used in this study. PEG was chosen as the ligand of interest due to its benign characteristics, low toxicity, and excellent biocompatibility [22] as well as its ability to form complexes with phenols and polyphenols through a more specific type of interaction: Hydrogen bonding [23; 24; 25]. It is hypothesized that, with the specificity of hydrogen bonding, polyphenols with a high number of hydroxyl groups can be recovered from grape pomace extract.