Journal of Chromatography A, 887 (2000) 327–337 www.elsevier.com / locate / chroma Towards the column bed stabilization of columns in capillary electroendosmotic chromatography Immobilization of microparticulate silica columns to a continuous bed a, a b b * Thomas Adam , Klaus K. Unger , Monika M. Dittmann , Gerard P. Rozing a ¨ ¨ Institut f ur Anorganische Chemie und Analytische Chemie, Johannes Gutenberg-Universitat, Duesbergweg 10 –14, 55099 Mainz, Germany b Hewlett-Packard GmbH, now Agilent Technologies, Waldbronn, Germany Abstract This article discusses a novel method generating a continuous bed inside the CEC column. The column bed composed of microparticulate reversed-phase silica is completely immobilized by a hydrothermal treatment using water for the immobilization process. This process eliminates the manufacture of frits of both ends of the column and all problems associated with their preparation. Fundamental studies on operational parameters will be presented such as the dependence of the immobilization on the column temperature, the type of stationary phase and the column back pressure. The immobilized CEC columns show the same high column efficiency as packed columns with frits.  2000 Elsevier Science B.V. All rights reserved. Keywords: Stationary phases, CEC; Immobilization; Electrochromatography; Silica, microparticulate 1. Introduction osmotic flow (EOF) transports the mobile phase and the solutes through the column. This type of flow has Capillary electrochromatography (CEC) has be- favourable properties compared to the viscous flow come a versatile, capillary separation technique used in an HPLC separation system. Flow velocity which combines attractive features of micro-high- differences in the axial direction leading to band performance liquid chromatography (HPLC), regard- broadening by Eddy diffusion are much smaller in ing the control of retention and selectivity by mobile electrical driven solvent transport than in HPLC. phase and stationary phase manipulation and of Further, the EOF is generated by the charge of the capillary electrophoresis (CE) regarding the high silica particles, as well as by the charges at the efficiency of separation [1–7]. In CEC the electro- capillary wall, in contrast to pressure-driven solvent transport. This allows the usage of much smaller particles or longer separation columns than in HPLC [3,8–11]. In CEC separation is achieved by solute– *Corresponding author. Bayer AG, PH-OP-Elb-QW, Geb. 302, surface interactions or partitioning of the solute Friedrich-Ebert-Strasse 117–300, D-42096 Wuppertal, Germany. between the mobile and the stationary phase. When Tel.: 149-202-36-7548; fax: 149-202-36-2633. E-mail address: thomas.adam.ta@bayer-ag.de (T. Adam) the solutes are charged, the separation is governed by 0021-9673 / 00 / $ – see front matter  2000 Elsevier Science B.V. All rights reserved. PII: S0021-9673(99)01330-8