Experiences with packed capillary electrochromatography at ambient pressure van den Bosch, S.E.; Heemstra, S.; Kraak, J.C.; Poppe, H. General rightsIt is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), other than for strictly personal, individual use, unless the work is under an open content license (like Creative Commons). Disclaimer/Complaints regulationsIf you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the Library know, stating your reasons. In case of a legitimate complaint, the Library will make the material inaccessible and/or remove it from the website. Please Ask the Library: http://uba.uva.nl/en/contact, or a letter to: Library of the University of Amsterdam, Secretariat, Singel 425, 1012 WP Amsterdam, The Netherlands. You will be contacted as soon as possible. AbstractThe practical execution of packed capillary electrochromatography is evaluated. The most serious problem is the generation of air bubbles in the system. This occurs especially in flits which were fabricated by glueing particles differing from the packing particles. No air bubbles were generated with frits which were prepared by locally sintering a narrow band of the reversed-phase packing by means of a heating filament, while flushing the column with water. In this way electrochromatography can be performed simply without pressurizing the buffer vials, providing the mobile phase is frequently degassed with helium. The performance under electrically driven conditions appears to be excellent and for 5 #m reversed-phase particles reduced plate heights down to 1.8 were achieved. Compared to pressure driven conditions, 25-40% smaller plate heights were obtained under electrically driven conditions.

The application of the electro-osmotic flow to force the mobile phase in packed capillary liquid chromatography looks very attractive from a theoretical point of view. Due to the plug flow profile less broadening of the bands by convective mixing will occur and larger efficiencies can be expected than under pressure conditions where the flow profile is parabolic. Moreover, the electro-osmotic flow is independent of the channel width and thus an acceptable flow-rate can be obtained in columns of common length packed with very small particles. The effect of the particle size of the reversed packing on the performance was investigated. The particle size ranged from 1.5 to 5 mm. The efficiency of the columns was measured under pressure and electrically driven conditions. All of the experiments with 3 and 5 mm ODS-Hypersil particles were performed with a home made system, with the electrode vials at ambient pressure. The experiments with 1.5 mm ODS-Chromspher particles were performed with a HP 3D CE (Hewlett Packard) system in which both electrode vials were equally pressurised at 10 bar.In Fig. 1 the effect of particle size on obtained plate height of pyrene as neutral compound with CEC is presented. As can be seen the plate height decreases with decreasing particle size in according with theory. With 3 and 5 mm particles the reduced plate height was about 2, but with the non-porous 1.5 mm ODS-Chromspher reduced plate height of 1.3 was observed. In order to avoid bubble formation with the 1.5 mm particles the two electrode vials has to be pressurised at 10 bar and 1-5 mmol/L sodium dodecyl sulfate (SDS) has to be added to the mobile phase. Fig. 2 shows a very fast and efficient separation of a mixture alkylbenzenes on the 1.5 mm ODS-Chromspher column.The capillaries packed with 1.5 mm ODS non-porous particles appeared to be extremely efficient and on a 24 cm long column about 120,000 plates were generated ($ 500,000 plates/m). The columns are quite stable and have been used for more than two months without loss in efficiency. #

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