Preparation of stationary phases for open-tubular capillary electrochromatography using the sol-gel method

Capillary electrochromatography requires the deposition of a stationary pha se inside the capillary. In this paper the sol-gel method is proposed for t his purpose. The gels were prepared externally and injected into a fused-si lica capillary, where anchorage to the capillary wall was possible through condensation reactions between the silanol groups of the capillary wall and the residual silanol groups the gel. Contrary to a commonly used practice, alkaline pretreatment of the inner capillary wall prior to the introductio n and anchoring of the gel was found to be only marginally effective in imp roving the mechanical stability of the column. The influence of various par ameters, such as the pH, the water content, the presence of alcohol (ethano l) on the formation of tetraethoxysilane (TEOS)-n-octyltriethoxysilane (C-8 -TEOS) hybrid gels of varied composition is discussed. The pH and the amoun t of water present were found to be the determining factors in the preparat ion of a stable gel with the desired mechanical and chromatographic propert ies. By carrying out the gel formation at 80 degrees C, capillary columns c ould be produced in 2.5 h. While an acidic pH was required during (external ) gel formation, subsequent treatment of the gel inside the capillary with an alkaline solution ('aging') was found to improve separation and stationa ry phase capacity significantly. The capillary columns were subsequently us ed to separate a mixture of polycyclic aromatic hydrocarbons in less than 3 min. (C) 2000 Elsevier Science B.V. All rights reserved.