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 .1. THEORY

New methods are described for the concentration of ionic analytes, par ticularly ampholytes, such as peptides and proteins. In most of these methods the sample is depleted (partially) of strong electrolytes conc omitantly with the concentration. The methods are based on the fact th at electrophoretic migration velocities decrease upon decreasing the a bsolute value of the zeta potential of a solute and the pore size of t he electrophoresis medium and upon increasing the cross section of the electrophoresis chamber, the viscosity and the electrical conductivit y of the electrophoresis medium. We have also utilized the zone-sharpe ning properties of displacement electrophoresis in combination with a hydrodynamic counter flow to create a stationary zone where the sample solutes can be collected continuously. In practice, the whole electro phoresis tube is filled with the sample solution to be concentrated. W hen a voltage is applied the solutes begin to migrate, but finally cea se to move as they approach the end of the tube, provided that the abo ve-mentioned parameters in that section of the tube have been given ap propriate values. By means of this technique the sample can be concent rated into a zone of a width of 0.2-0.5 mm. Accordingly, a 400-1000 fo ld concentration is obtained when a 200 mm long tube is filled complet ely with the sample and still more if also an electrode vessel (or a v essel connected to this electrode vessel) is loaded with sample. The n arrow sample zone can be withdrawn from the tube and subjected to furt her studies or used as a starting zone for an in-tube zone electrophor esis. The tendency for broadening of the very narrow starting zone dur ing the initial phase of this electrophoresis step can be counteracted by a short mobilization step involving displacement electrophoresis, electrophoresis in a steep pH gradient, or on-tube dialysis against a (diluted) buffer. This step can be omitted when the concentration is a ccomplished by a combination of displacement electrophoresis and a cou nter flow. In Part II we show how the theory developed in this paper c an be utilized practically.