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

• Published in: Journal of Chromatography A Vol. 1021; no. 1; pp. 61 - 70
• Main Authors: Bruch, Martha D, Fatunmbi, Hafeez O
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 22.12.2003; Elsevier
• Subjects: Amine ligands; Amines - chemistry; Analytical chemistry; Chemistry; Chromatographic methods and physical methods associated with chromatography; Cross polarization–magic-angle spinning; Cross-linking; Exact sciences and technology; Ligands; Magnetic Resonance Spectroscopy - methods; Nuclear magnetic resonance spectroscopy; Other chromatographic methods; Silica; Silica Gel; Silicon Dioxide - chemistry; Stationary phases, LC; Cross polarization–magic-angle spinning; Nuclear magnetic resonance spectroscopy; Amine ligands; Cross-linking; Silica; Stationary phases, LC; Cross polarization; HPLC chromatography; NMR spectrometry; Surface analysis; Magic angle; Chemical modification; Silicon 29; LC; Cross-linking; Amine ligands; Silica; Silica gel; Carbon 13; Cross polarization-magic-angle spinning; Nuclear magnetic resonance spectroscopy; Stationary phases; Modified material; Stationary phase
• ISSN: 0021-9673
• DOI: 10.1016/j.chroma.2003.08.093

Different approaches for quantitative analysis by 29Si and 13C CP/MAS nuclear magnetic resonance (NMR) of silica gel chemically modified by a mixture of long and short chain amines, –(O) 3Si(CH 2) 3N(CH 3) 2(CH 2) 13CH 3 and –(O) 3Si(CH 2) 3N(CH 3) 3, are compared to elemental analysis. Unlike 29Si NMR, variable contact time data are necessary for accurate quantitative analysis by 13C 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.