Journal of Chromatography A, 916 (2001) 89–99 www.elsevier.com / locate / chroma Extremely high electric field strengths in non-aqueous capillary electrophoresis * ¨ ¨ Sami Palonen, Matti Jussila, Simo P. Porras, Tuulia Hyotylainen, Marja-Liisa Riekkola Laboratory of Analytical Chemistry, Department of Chemistry, P .O. Box 55, FIN-00014 University of Helsinki, Helsinki, Finland Abstract The influence of high electric field strength on the separation of basic analytes in non-aqueous alcohol background electrolyte (BGE) solutions was investigated. Increasing the separation voltage in capillary electrophoresis (CE) may be advantageous if the conductivity of the BGE solution is low enough to allow fast separations without excessive Joule heating or band broadening. The voltage range tested was 20–60 kV with methanol and ethanol, and 25–60 kV with propanol and 21 21 butanol as solvent for BGE. The resulting electric field strengths ranged from 660 V cm to 2000 V cm . Experiments were made with a special laboratory constructed CE instrument. The separation efficiency vs. voltage curve was found to vary with the alcohol BGE solution. The increase in voltage decreased the separation efficiency in the case of methanol BGE solution, but with the other BGEs a clear efficiency maximum was obtained above 30 kV. The highest separation efficiencies were achieved with propanol BGE solution, where the efficiency maximum was reached at 45 kV. However, reasonable efficiency was achieved even at 60 kV. The extent of Joule heating was determined by calculating the temperature inside the capillary and the observed plate heights were interpreted in terms of the Van Deemter equation. The decrease in the separation efficiency with higher voltage was attributed mainly to Joule heating in the case of methanol and ethanol BGE solution and to the analyte adsorption on the capillary wall with propanol and butanol BGE solutions.  2001 Elsevier Science B.V. All rights reserved. Keywords: Non-aqueous capillary electrophoresis; Electric field strength; Joule heating; Adsorption; Efficiency; Background electrolyte composition; Potential 1. Introduction associated with Joule heating becomes severe above 30 kV because of the high current in the capillary. Capillary electrophoresis (CE) separations are Hence, for most CE-users, a voltage maximum of 30 usually performed with electrical potentials no great- kV has been considered acceptable. er than 30 kV. The potential range available in If only longitudinal diffusion is contributing to the commercial capillary electrophoresis instruments is plate height, the separation efficiency increases often limited to 230 kV to 130 kV, mainly because linearly with the applied potential: of electrical insulation problems and safety consid- ( m 1 m )L U erations. Additionally, with aqueous background ep eo det ]]]]] N 5 (1) electrolyte (BGE) solutions, the band broadening 2DL tot where N is the plate number, U is the applied *Corresponding author. Fax: 1358-9-191-50253. separation potential, and L and L are the capil- E-mail address: marja-liisa.riekkola@helsinki.fi (M.-L. Riek- det tot kola). lary length to the detection window and the total 0021-9673 / 01 / $ – see front matter  2001 Elsevier Science B.V. All rights reserved. PII: S0021-9673(01)00557-X