Publications by authors named "Norbert Welsch"
Silica gels modified with n-alkyl chains (n = 18, 30) are prepared by two different synthetic routes and are examined by variable temperature FTIR and solid-state NMR spectroscopy. HPLC measurements of SRM 869, cis/trans ss-carotene isomers and xanthophylls isomers confirm the dependence of the separation mechanism on the alkyl chain length and the synthetic routes. The determination of the silane functionality and degree of cross-linking of silane ligands on the silica surface is achieved by 29Si CP/MAS NMR measurements.
View Article and Find Full Text PDFSiO2 surfaces-silica gel particles and silica wafers-were modified by covalently immobilizing three poly(ethylene-co-acrylic acid) copolymers, (-CH2CH2-)x[CH2CH/(CO2H)-]y, with different chain lengths and mass fractions of acrylic acid. 13C solid-state NMR spectroscopy on the modified silica gel particles revealed both mobile gauche and rigid trans aligned alkyl chains in the copolymers. For copolymers attached to silica wafers via a 3-aminopropyltriethoxysilane spacer molecule, ellipsometric measurements revealed a mean value of the layer thickness distribution of 6.
View Article and Find Full Text PDFArticle Synopsis
- Three types of poly(ethylene-co-acrylic) acid copolymers were immobilized on silica to create stationary phases for chromatography, using different spacer molecules.
- The study observed that stationary phases with more rigid alkyl chain structures showed better selectivity for certain carotenoid isomers, like beta-carotene and xanthophylls.
- This research demonstrated that the separation of analytes was influenced by polar interactions and the conformation of alkyl chains, as evidenced by NMR spectroscopy results.