[3-(Methacryloxy)propyl]trimethoxysilane-based monolithic stationary phases for capillary-scale chromatography and their characterization by contactless conductivity detection and solid-state NMR spectroscopy

Abstract This work describes the preparation, characterization and application of monolithic stationary phases for capillary-scale chromatography. The columns were prepared by polymerization of [3-(methacryloxy)propyl]trimethoxysilane (MPTMS) monomer in two consecutive steps: i) sol–gel process and ii) photoinitiated radical addition. The photopolymerization was carried out in 100 μm i.d. UV-transparent coating fused silica capillaries. The columns were applied in the qualitative separation of five polycyclic aromatic hydrocarbons (PAH) by both capillary liquid chromatography (nano-LC) and capillary electrochromatography (CEC) in a capillary electrophoresis equipment. In an attempt to improve the separation of the PAHs, the stationary phase was modified by incorporating benzyl methacrylate (BM) as a comonomer in the MPTMS-based polymer structure, but no improvement was observed. The physical homogeneity of the columns was evaluated by using an optical microscope and a capacitively coupled contactless conductivity detector (C4D) as a non-invasive scanner moving longitudinally along the capillary. The chemical characterization of the polymer was done by both 13C and 29Si solid-state nuclear magnetic resonance spectroscopy (SSNMR). It was possible to propose a carbon chain structure and the substitution degree of the silyl group indicating the cross-linking of the polymer chains through the formation of dimers and trimers by condensation of the alkoxysilane groups.