Extremely high electric field strengths in non-aqueous capillary electrophoresis

The influence of high electric field strength on the separation of basic an alytes in non-aqueous alcohol background electrolyte (BGE) solutions was in vestigated. Increasing the separation voltage in capillary electrophoresis (CE) may be advantageous if the conductivity of the BGE solution is low eno ugh to allow fast separations without excessive Joule heating or band broad ening. The voltage range tested was 20-60 kV with methanol and ethanol, and 25-60 kV with propanol and butanol as solvent for BGE. The resulting elect ric field strengths ranged from 660 V cm(-1) to 2000 V cm(-1). Experiments were made with a special laboratory constructed CE: instrument. The separat ion efficiency vs. voltage curve was found to vary with the alcohol BGE sol ution. The increase in voltage decreased the separation efficiency in the c ase of methanol BGE solution. but with the other BGEs a clear efficiency ma ximum was obtained above 30 kV. The highest separation efficiencies were ac hieved with propanol BGE solution, where the efficiency maximum was reached at 45 kV However, reasonable efficiency was achieved even at 60 kV. The ex tent of Joule heating was determined by calculating the temperature inside the capillary and the observed plate heights were interpreted in terms of t he Van Deemter equation. The decrease in the separation efficiency with hig her voltage was attributed mainly to Joule heating in the case of methanol and ethanol BGE solution and to the analyte adsorption on the capillary wal l with propanol and butanol BGE solutions. (C) 2001 Elsevier Science B.V. A ll rights reserved.