Silver (I)-dimercaptotriazine functionalized silica: A highly selective liquid chromatography stationary phase targeting unsaturated molecules

• Published in: Journal of Chromatography A 2021-05, Vol.1645, p.462122, Article 462122
• Main Authors: Liao, Sian, Dillon, James T., Huang, Cancan, Santos, Ewerton, Huang, Yongsong
• Format: Article
• Language: English
• Subjects: Lipid analysis; Silver ion chromatography; Silver(I)-dimercaptotriazine; Silver-thiolate chromatography; Van't Hoff plots
• ISSN: 0021-9673
• DOI: 10.1016/j.chroma.2021.462122

•Ag-DMT shows higher retention factors, peak resolutions and capacities than Ag-MP.•Ag-DMT is highly selective to number, position and geometry of C=C bonds.•Ag-DMT also interacts chromatographically with alkyl structures.•Ag-DMT has high stability over repeated uses.•Ag-DMT forms more stable complexes with olefins than Ag-MP. Silver(I)-mercaptopropyl (Ag-MP) functionalized silica gel has demonstrated its effectiveness in separating various unsaturated organic compounds including unsaturated fatty acid ethyl esters (FAEEs), triglycerols (TAGs) and long-chain alkyl ketones (alkenones). While Ag-MP stationary phase displays many advantages over the conventional silver ion-impregnated silica gel (e.g., stability, high recovery, etc.), potential drawbacks of Ag-MP include relatively low retentions for unsaturated molecules, which could limit chromatographic resolutions under certain circumstances. In this study, we evaluate a new silver-thiolate stationary phase: silver(I)-dimercaptotriazine (Ag-DMT) functionalized silica gel targeting the separation of unsaturated compounds. We show Ag-DMT affords substantially higher retention factors, peak resolutions and capacities for TAGs and FAEEs than Ag-MP does. Ag-DMT also yields higher purity eicosapentaenoic acid (EPA) from fish oil FAEE mixtures than Ag-MP. In addition, Ag-DMT resolves double bond positional and cis/trans-isomers of C18:1 fatty acid methyl esters (FAMEs) as well as unsaturated methyl/ethyl alkenones with different number of double bonds. Based on van't Hoff plots, enthalpy changes during the adsorption of unsaturated FAEEs onto Ag-DMT are ~2 times higher than those on Ag-MP. Such difference may be attributed to the stronger electron-withdrawing effect of the thiol group on DMT, which results in more positively charged silver ions hence greater interactions with unsaturated molecules. The stronger interaction between double bonds and Ag-DMT is further corroborated by density-functional theory (DFT) calculations. Ag-DMT shows its high stability for repeated uses in the separation of TAGs over 319 runs, with peak resolutions decreasing by < 3%. Collectively, our data demonstrate the exceptionally high efficiency of Ag-DMT column for separating unsaturated molecules.