Solvation, interaction and dynamics of xenon atoms in HPLC column materials studied by variable-temperature dependent 129Xe, 1H–129Xe cross-polarization, and two-dimensional exchange NMR experiments
Xenon NMR is a useful method for probing structure and dynamics of micro-porous materials due to the sensitivity of xenon’s chemical shifts to its local interactions, and the diffusion property of xenon atoms. Here, we report a study of solvation, interaction and diffusion of xenon atoms inside the HPLC column materials, Zorbax SB-C18 and XDB-C18 which were made of siloxane surface coatings of porous silica, by variable-temperature dependent (VT) 129Xe, 1H–129Xe cross-polarization (CP), and two-dimensional exchange (2D EXSY) NMR experiments. The VT NMR experiment showed the solvation and dynamics of xenon atoms in the column materials. The CP experiment at low temperature provided evidence for probing the direct interaction of xenon atoms with the hydrocarbon chains of the stationary phase, and helped for assigning the 129Xe peaks in the VT NMR spectra. The 2D EXSY NMR experimental result showed the diffusion of xenon atoms within the accessible spaces in the column materials. Combined with our previous study, a full picture of xenon’s behavior inside the column materials has been described. This study provides a basic understanding of xenon NMR of the column materials, which enables us to conduct further investigation of retention mechanisms of column materials in terms of molecular interaction and diffusion by xenon NMR method.