ELECTROMIGRATION INJECTION FROM A SMALL LOOP IN CAPILLARY ELECTROPHORESIS

Capillary electrophoresis (CE) is now clearly the separation technique of the decade. One aspect that is still in need of improvement is con centration sensitivity, especially when CE is used in conjunction with on-column UV-visible absorptiometry, by far the most common practice. Electromigration injection (EI) is among the most prominent technique s in CE that serves to improve the attainable limits of detection; it is also the most convenient and simplest of all injection modes. Unfor tunately, EI is affected both from sample to sample (the amount of an analyte introduced depends on sample conductance) and from analyte to analyte within a sample (the introduction is strongly biased on analyt e electrical mobility). Previously we have shown the utility of small loops affixed at the tip of a capillary (Anal. Chem. 1995, 67, 3853-38 60; 1996, 68, 1164-1168). The present paper shows that there are remar kable advantages to be gained from forming a film of the sample soluti on on a wire loop and using the loop itself as the high-voltage electr ode to perform electromigration from a very small sample volume. The s ample constituents can-be essentially exhaustively electromigrated fro m this volume in less than 1 min, and the mobility induced bias is dra matically lowered. The observed experimental behavior agrees with theo retical models.