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

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 um 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 ((CD)-D-4) as a non-invasive scanner moving longitudinally along the capillary. The chemical characterization of the polymer was done by both C-13 and Si-29 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.

Automated summary

This study prepared monolithic stationary phases for capillary chromatography by polymerizing MPTMS monomer, applied them in separating PAHs, and attempted to improve the stationary phase by incorporating BM as a comonomer. The physical homogeneity of the columns was evaluated using an optical microscope and a conductivity detector, while the chemical characterization was done using solid-state NMR spectroscopy.