Concentration and fractionation by isoelectric trapping in a micropreparative-scale multicompartmental electrolyzer having orthogonal pH gradients. Part 1.

A multicompartmental electrolyzer called ConFrac has been developed and tested for micropreparative-scale isoelectric trapping separations. ConFrac contains n separate, minimalistic isoelectric trapping core units, each with a separate anode compartment, anodic flow-through compartment, collection compartment, cathodic flow-through compartment and a shared cathode compartment. The collection compartments are all isolated from each other and have volumes of 100 μL each. The liquid held in the collection compartments is stagnant. The respective anodic and cathodic flow-through compartments are hydraulically serially connected to each other by flexible, minimum-length, narrow internal diameter tubes. The respective feed solutions whose volumes are larger and variable are recirculated through the serially connected flow-through compartments. Poly(vinyl alcohol)-based buffering membranes are placed between the anode compartments, anodic flow-through compartments, collection compartments, cathodic flow-through compartments and cathode compartment. The membranes establish two orthogonal pH gradients in ConFrac. The primary pH gradient is parallel with the direction of the recirculating flows and orthogonal to that of the electric field. The secondary pH gradient is parallel with the direction of the electric field and orthogonal to that of the recirculating flows. Since the recirculating liquids are kept in thermostated reservoirs and the residence times in the flow-through compartments are shorter than 2 s, ConFrac can tolerate power loads as high as 2 W without overheating the solutions. The operation and performance of ConFrac has been quantitatively characterized: four 25 μM ampholytic components were isolated from 5 mL of feed solution in 20 min and their concentration increased approximately 50-fold.