Nuclear magnetic resonance analysis of silica gel surfaces modified with mixed, amine-containing ligands

Different approaches for quantitative analysis by Si-29 and C-13 CP/MAS nuclear magnetic resonance (NMR) of silica gel chemically modified by a mixture of long and short chain amines, -(O)(3)Si(CH2)(3)N(CH3)(2)(CH2)(13)CH3 and -(O)(3)Si(CH2)(3)N(CH3)(3), are compared to elemental analysis. Unlike Si-29 NMR, variable contact time data are necessary for accurate quantitative analysis by C-13 NMR. Surprisingly, spectral overlap does not interfere with this approach. Surfaces prepared from reaction mixtures that consisted of 67 and 33% (v/v) long chain are found to actually contain 37 and 16% long chain amines, respectively. The mixed phase surfaces have more extensive cross-linking and fewer unreacted hydroxyls than single phase surfaces. (C) 2003 Elsevier B.V. All rights reserved.