Capillary electrophoresis with wide-bore capillaries and non-aqueous media

Abstract

A major drawback of capillary electrophoresis is that its use for semi-preparative purposes is problematic. To overcome the problems associated with wide-bore capillaries, non-aqueous background electrolyte instead of aqueous buffers was used. The effect of the capillary diameter on capillary electrophoretic separation was investigated in ethanol–acetonitrile–acetic acid (50:49:1, v/v) containing 20 m M ammonium acetate. This buffer allowed the use of wider capillaries and higher electric field strength than the corresponding buffer containing water in place of ethanol and acetonitrile. Increasing the internal diameter of the capillary from 50 to 200 μm allowed a 16-fold increase in the sample load at the same ratio of injected volume to total volume. In wide-bore capillaries the difference between the inlet and outlet buffer level leads to siphoning, which has a marked effect on the apparent electroosmotic velocity and the efficiency of the separation. The effect of the physical properties of the solvent on siphoning is discussed. Our results indicate that non-aqueous media may have a major role in semi-preparative capillary electrophoresis.