Fluorinated Carbon Chain Research Articles

Fluorinated ligands in HPLC

Summary The chromatographic behaviour of C6F5(CH2)3SiCI 3, C6Hs(CH2)3SiCI 3, CF3(CF2)7CH2CH2SiCI 3 and n-CloH21SiCI 3 as well as the bonding of these ligands to silica is described. Phases with partially fluorinated ligands show entirely different chromatographic characteristics to analogous phases, where hydrogen replaces fluorine. The silica with the pentafluorophenyl-3-npropyI-C6F5(CH2)3-1igand has higher k'-values and a better selectivity for aromatic hydrocarbons than that with phenyl-3-n-propyl C6Hs(CH2)3-groups, whereas the phase with the fluorinated carbon chain is less useful than the silica modified with n-decyltrichlorosilane n-CloHmSiCI 3. The first effect can be explained by complex formation, and the second may be due to a different contact area between the ligand and the solute. The normal hydrocarbon chains hinder each other sterically and expose many adsorption sites, in contrast the perfluorinated chains are sterically fixed and are the first example of real brushes in HPLC.

Fluorinated lignands in HPLC

The chromatographic behaviour of C6F5(CH2)3SiCl3, C6H5(CH2)3SiCl3, CF3(CF2)7CH2CH2SiCl3 and n-C10H21SiCl3 as well as the bonding of these ligands to silica is described. Phases with partially fluorinated ligands show entirely different chromatographic characteristics to analogous phases, where hydrogen replaces fluorine. The silica with the pentafluorophenyl-3-n-propyl-C6F5(CH2)3-ligand has higher k′-values and a better selectivity for aromatic hydrocarbons than that with phenyl-3-n-propyl C6H5(CH2)3-groups, whereas the phase with the fluorinated carbon chain is less useful than the silica modified with n-decyltrichlorosilane n-C10H21SiCl3. The first effect can be explained by complex formation, and the second may be due to a different contact area between the ligand and the solute. The normal hydrocarbon chains hinder each other sterically and expose many adsorption sites, in contrast the perfluorinated chains are sterically fixed and are the first example of “real brushes” in HPLC.