COMBINED LIQUID-LIQUID ELECTROEXTRACTION AND ISOTACHOPHORESIS AS A FAST ONLINE FOCUSING STEP IN CAPILLARY ELECTROPHORESIS

Combined liquid-liquid electroextraction and isotachophoresis as a fast on-line focusing step in capillary electrophoresis is described. Owing to the limited conductivity of the organic phase, high electric field strengths can be applied, resulting in high migration rates. Liquid-liquid electroextraction is used to focus the analyte ions from a large organic sample into a small volume in the terminating buffer zone, just above the liquid-liquid interface. Simultaneously, isotachophoresis is used to focus the analyte ions between the terminating buffer and the leading buffer. A steady state is reached within a few minutes, as isotachophoresis starts with a small sample volume. On-line capillary zone electrophoresis is used for the separation of the analytes. Propantheline, neostigmine, salbutamol and terbutaline were used as model compounds, and crystal violet was used to visualize the process for tuning the system. Concentration detection limits of pure solutions down to 10(-9)-10(-10) mol/l for the model compounds were obtained using simple UV absorbance detection.