Molecular Selectivity\nof a pH-Tunable Lecithin-Modified\nZirconia Stationary Phase

We synthesized lecithin-modified zirconia (LMZ) as an\nadsorbent,\nsolid-phase extractant, and stationary phase for organic compounds\nsuch as organic acids or amino acids. The molecular selectivity of\nLMZ was evaluated through high-performance liquid chromatography (HPLC).\nLMZ exhibits electrostatic and hydrophobic interactions with organic\ncompounds that depend on the pH of the mobile phase. Zirconia was\nchosen because of its strong affinity for phosphate-containing compounds.\nSoybean lecithin, a model phospholipid, was directly and stably grafted\nonto zirconia particles through a Lewis acid–base reaction\nto form LMZ. The presence of lecithin on the zirconia surface was\nconfirmed through solid-state analytical techniques such as confocal\nlaser scanning microscopy and thermogravimetric analysis. The molecular\nselectivity of LMZ was assessed by measuring the retention behavior\nof aromatic compounds and amino acids on an LMZ column using HPLC.\nLMZ recognized analyte organic compounds through both electrostatic\nand hydrophobic effects that depended on the pH of the mobile phase.\nInterestingly, LMZ could clearly discriminate between electrostatic\ninteractions with hydrophilic compounds such as amino acids and hydrophobic\ninteractions with hydrophobic compounds such as aromatics. The specific\nmolecular selectivity achieved using LMZ was attributed to not only\nthe zirconia substrate but also the ionic and alkyl functional groups\nof lecithin.