Abstract
Information on the surface properties of three novel chemically bonded phase packing materials for High performance liquid chromatography (HPLC) were obtained using spectra obtained by solid state cross-polarization (CP) magic-angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopic experiments for the 29Si, and 13C nuclei. These packing materials were: Cogent bidentate C18 bonded to type-C silica, hybrid packing materials XTerra MS C18, and XBridge Prep. C18. The spectra obtained using cross-polarization magic angle spinning (CP-MAS) on the Cogent bidentate C18 bonded to type-C silica show the surface to be densely populated with hydride groups (Si-H), with a relative surface coverage exceeding 80%. The hybrid packing materials XTerra and XBridge gave spectra that reveal the silicon atoms to be bonded to organic moieties embedded in the molecular structure of these materials with over 90% of the alkyl silicon atoms found within the completely condensed silicon environments. The hydrolytic stability of these materials were investigated in acidic aqueous solutions at pHs of 7.0 and 3.0, and it was found that while the samples of XTerra and XBridge were not affected by hydrolysis at this pH range, the sample of Cogent lost a significant proportion of its Si-H groups after five days of treatment in acidic aqueous solution.
Highlights
High performance liquid chromatography (HPLC) remains one of the most widely used separation methods in chemical analysis
It is estimated that 80% of all separations made in pharmaceutical, biomedical, and, environmental analyses are performed with HPLC [6]
This explains why there is a constant interest in the preparation and evaluation of new packing materials for HPLC columns, as well as in the optimization of chromatographic systems [7]
Summary
High performance liquid chromatography (HPLC) remains one of the most widely used separation methods in chemical analysis. Even after a surface has been derivatized, numerous residual silanols remain on the unbonded regions of the surface, in part because silica particles have a complex structure of many small pores (sizes range from 90–135 Ǻ), and bulky reagents like octadecylsilane have a limited ability to reach their surface because some silanol groups are hindered by previously bonded ligands or have a low reactivity. This is undesirable if it contributes to unwanted interactions like the electrostatic attraction of analytes by these Si-OH groups. Ion-exchange interactions of basic compounds with acidic residual silanols can cause tailing of their peaks [8]
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