NEW APPROACHES TO CONCENTRATION ON A MICROLITER SCALE OF DILUTE SAMPLES, PARTICULARLY BIOPOLYMERS WITH SPECIAL REFERENCE TO ANALYSIS OF PEPTIDES AND PROTEINS BY CAPILLARY ELECTROPHORESIS .2. APPLICATIONS

On theoretical grounds several approaches for the concentration of ionic solutes are suggested in ref. 1. The methods are of general applicability. In this paper we describe how they can be employed in high-performance capillary electrophoresis (HPCE) for 1000-fold manual and automated on-line concentration from microliters down to nanoliters. The risk that the solutes may escape detection -the obvious disadvantage of HPCE- is, accordingly, reduced considerably. Briefly, the whole capillary (and for more than 1000-fold concentration also an electrode vessel or a vessel in contact with an electrode vessel) is filled with the dilute sample solution. The sample becomes concentrated as it migrates toward a pH gradient, a small-pore gel, a dialysis tubing attached to one end of the capillary, or by displacement electrophoresis combined with a hydrodynamic counterflow. These concentration steps (except the last) require a short mobilization step to prevent the narrow, concentrated sample zone from broadening in the initial phase of the final analysis step (free zone electrophoresis).