Solid-state NMR and FT IR studies on chromatographic column materials

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The development of alkyl bonded stationary phases has significantly contributed to the rise of reversed-phase high-performance liquid chromatography as the leading method in the field. The conformational order of alkyl chain moieties is a key factor in determining efficiency and selectivity during chromatographic separations. Understanding this conformational order at the molecular level is essential for optimizing chromatographic applications. This work utilizes FT IR and solid-state NMR spectroscopic techniques to investigate the conformational order and mobility of alkyl chain segments attached to solid surfaces. Various factors, including solid supports, pressure, surface coverage, synthetic routes, and solvents across a broad temperature range, affect the conformational order of these alkyl chains. FT IR data for C₃0 SAMs indicate that the solid substrate significantly influences the conformational state of attached alkyl chains. In the case of commercial DiamondBond-C₁8 phases, alkyl chains bonded to the graphite layer demonstrate greater conformational order than those in standard column materials. Additionally, C₁8 alkyl modified silica gels with higher surface coverage show improved conformational order compared to those with lower coverage. Notably, interactions between C₁8 phases and solvents lead to marked changes in conformational order, while applying pressure reduces conformational disorder. Overall, these findi