Sensitivity enhancement effect in off-column detection for capillary electrophoresis

Abstract

The sensitivity enhancement effect in off-column detection for capillary electrophoresis was investigated. A capillary is divided into a separation and coupling capillaries by an on-column fracture coated with cellulose acetate porous polymer. The electroosmotic flow produced in the separation capillary acts as a pump and makes the buffer fluid flow through the coupling capillary. In the separation capillary, sample ions are induced to proceed not only by the buffer fluid flow but also by electrophoretic migration. On the other hand, in the coupling capillary, ions move only by the buffer fluid flow. The difference in the migration velocity of the sample ions between the separation and coupling capillaries results in concentration (for a cationic sample) or dilution (for an anionic sample) of the sample zone after passing through the fracture. Two cation dyes, rhodamine B and safranine O, were used as model samples. An off-column absorbance detection method with a 542.8-nm He-Ne laser as light source was used for demonstration of the sensitivity enhancement effect. The maximum concentration factor observed in the experiments was about 4.7 for Safranine O. The factors affecting the enhancement factor in off-column detection with a practical conductive joint are discussed.