Monolithic Silica Capillary Columns with Improved Retention and Selectivity for Amino Acids

A strategy for the preparation of silica-based monolithic capillary columns (150 × 0.1 mm) with high selectivity to amino acids is presented. The zwitterionic columns were prepared by coating the silica monolith with [2-(methacryloyloxy)ethyl]-dimethyl-(3-sulfopropyl)-ammonium hydroxide via 3-(trimethoxysilyl)propyl methacrylate. The columns were evaluated under isocratic conditions in hydrophilic interaction liquid chromatography. The best separation of amino acids was obtained on the monolithic column prepared by a stepwise modification procedure where the modification step was repeated four times. The mixture of fifteen amino acids was separated within 13 min using the mobile phase consisting of 75% acetonitrile and 25% 5 mmol/L ammonium acetate at pH 4.5.

Silica Monolithic Capillary Columns for Hilic Separations

The monolithic capillary columns (0.1 mm x 150 mm) prepared by the acidic hydrolysis of tetramethoxysilane (TMOS) in the presence of polyethylene glycol (PEG) and urea were modified by zwitterionic stationary phases and evaluated under HILIC separation conditions by employing a mixture containing nucleosides and nucleotides. The polymeric layer of zwitterions did not affect the high separation efficiency of the original silica monolith. The prepared zwitterionic columns exhibited high separation efficiencies in a range 61,000-289,000 theoretical plates/m for a 2- methacryloyloxyethyl phosphorylcholine-based stationary phase and in a range 59,000-135,000 theoretical plates/m for a [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide-based stationary phase under optimal separation conditions. The grafted layer of zwitterions on the silica monolithic surface also significantly improved the separation selectivity to compounds of interest

Monolithic capillary columns consisting of poly(glycidyl methacrylate-co-ethylene glycol dimethacrylate) and their diol derivatives with incorporated hydroxyl functionalized multiwalled carbon nanotubes for reversed-phase capillary electrochromatography

Schemes for the preparation of the poly(GMA-co-EDMA) monolith and its diol monolith derivative with physically and covalently entrapped OH-MWCNTs.