Chromatographic characterisation of monolithic capillary columns for liquid chromatography based on methyltrimethoxysilane as sole precursor

A set of monolithic capillary columns for liquid chromatography, synthesized according to a recently developed protocol which uses methyltrimethoxysilane (MTMS) as a sole precursor, is characterised by various chromatographic tests to assess its physico-chemical properties. The new stationary phase material shows a hydrophobicity (assessed on the basis of methylene selectivity) comparable to commercial C8 columns. The MTMS-based columns exhibit a reduced affinity towards planar molecules such as PAHs, compared to C18 modified columns, which can be explained by a retention mechanism that is more governed by adsorption rather than partitioning. In comparison to commercial products an only moderate silanol activity was observed, even without any endcapping procedure applied. Selectivity between hydrophobic test compounds showed to be uniform between the columns investigated in this study, whereas retention factors differed up to 20% (batch-to-batch reproducibility) between columns produced under the same conditions. For most of the materials investigated in this study, size exclusion towards even only slightly larger molecules such as triphenylene was observed. It was demonstrated that inclusion of a micelle-forming detergent such as Brij in the synthetic protocol could partially overcome this problem.