Histidine-functionalized silica and its copper complex as stationary phases for capillary electrochromatography

A histidine-functionalized silica was prepared by covalent bonding of the f unctional groups to silane-treated silica gel. Conversion of functional gro ups was confirmed by infrared (IR) spectra, elemental analysis, and potenti ometry. The functionality of the silica gel is 0.293 mmol g(-1). The coordi nation behavior of the histidine-functionalized silica was investigated by metal capacity and electron paramagnetic resonance (EPR). EPR measurements at different copper loadings were made. The results showed that the copper histidine complex might be distorted tetragonal. Both histidine-functionali zed silica and its copper complex were employed as stationary phases for pa cked capillary electrochromatography (CEC). Electrical current was found he lpful for evaluating the properties of frit construction and the stationary phase packing. Test samples include neutral compounds, inorganic anions an d organic anions. Factors influencing the separation behavior have been stu died. With copper-histidine functionalized silica under the condition of ci trate buffer (10 mm, pH 4.0) and applied voltage of -20 kV, the separation of benzoic acid, D- and L-mandelic acid, phthalic acid and salicylic acid c ould be achieved within 12 min. The column efficiency for these acids was m ore than 1.2 x 10(5) plates m(-1), except salicylic acid.