A novel sol-gel calix[4]arene-modified capillary column for open-tubular capillary electrochromatography

A novel open-tubular CEC (OT-CEC) column was prepared by immobilized 5,11,17,23-tetra-tert-butyl-25,27-diethoxy-26,28-dihydroxy-calix[4]arene (Calix[4]) on fused-silica capillary column with sol-gel technology. Calix[4] was initially reacted with gamma-glycidoxypropyltrimethoxysilane (KH-560) to form a new sol-gel precursor (calix[4]-KH-560), and then mixed with another precursor, namely tetraethoxysilane (TEOS). After hydrolysis and condensation, a sol-gel matrix was obtained, in which calix[4] was incorporated. Successful calix[4]-modified sol-gel coating was suggested by infrared (IR) spectra and greatly decreased EOF. In comparison with OT columns prepared by the sol-gel method with TEOS and KH-560 only, the calix[4]-modified sol-gel column showed greatly improved separation of isomeric toluidines, nitrophenols, picolines and neurotransmitters with structural similarity. Migration time and theoretical plate number reproducibility were satisfactory with RSDs less than 1 and 6% each for within column runs and not more than 3 and 7% each for column-to-column measurements, using toluidine and nitrophenol isomers as test solutes on this column. High separation efficiencies (96,000-300,000 plates/m) for basic toluidine isomers were obtained. This column was also successfully employed to combine extraction procedure for the determination of dopamine (DA) and norepinephrine (NE) in Portulaca oleracea L. The recoveries of DA and NE were 93.3 and 94.2%, respectively.