Fundamental study of residual silanol populations on alkylsilane-derivatized silica surfaces
| Autor: | J.W. de Haan, C.A.M.G. Cramers, Alex B. Scholten, Henk A. Claessens, L.J.M. van de Ven |
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| Přispěvatelé: | Chemical Engineering and Chemistry, Materials and Interface Chemistry, Inorganic Materials & Catalysis |
| Jazyk: | angličtina |
| Rok vydání: | 1996 |
| Předmět: |
Fundamental study
Magic angle Chromatography Chemistry Cross polarization Surfaces and Interfaces Reversed-phase chromatography Condensed Matter Physics High-performance liquid chromatography Silanol chemistry.chemical_compound Phase (matter) Electrochemistry Surface modification General Materials Science Spectroscopy |
| Zdroj: | Langmuir, 12(20), 4741-4747. American Chemical Society |
| ISSN: | 1520-5827 0743-7463 |
| Popis: | Two commercially available reversed phases for high-performance liquid chromatography (one dimethyl-n-octadecylsilane phase and one di-isobutyl-n-octadecylsilane phase) and the native silica substrate were subjected to deuterium exchange in a mobile phase-like medium of acetonitrile and deuterium oxide (90/10, v/v). 29Si cross-polarization magic-angle-spinning (CP MAS) NMR was used to obtain information on the amounts and relaxation behavior of the internal silanols of the silica substrate, and the residual silanols of the alkylsilane-derivatized phases. Consequences for the correlation of silanol 29Si CP MAS NMR data and chromatography are discussed. Detection of deuterated silanol (SiOD) signals in 29Si CP MAS NMR of deuterium-exchanged phases depends on a transfer of magnetization (cross-polarization) from silane protons to silanol silicon atoms. It is concluded that a large portion of the residual silanol NMR signal of the phases stems from internal silanols and from silanols that are spatially very close to an alkylsilane attachment site. The former are considered chromatographically irrelevant while the latter are assumed to be inaccessible for analytes during the chromatographic separation process for reasons of steric constraints. One bulky di-isobutyl-n-octadecylsilane is capable of cross-polarizing proton magnetization to 0.8 residual surface silanols, whereas this is only 0.3 for the conventional octadecylsilane with dimethyl side groups. However, the lower surface concentration of bulky alkylsilanes leaves more space for free, unhindered silanols. The most important factor determining the relaxation behavior of the residual silanol NMR signal is the mobility of the octadecylsilane side chains, bulky silanes having the larger mobility quenching effect on residual silanols. |
| Databáze: | OpenAIRE |
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