A MICROMETHOD FOR CONCENTRATION AND DESALTING UTILIZING A HOLLOW-FIBER, WITH SPECIAL REFERENCE TO CAPILLARY ELECTROPHORESIS

Concentration of solutes in small volumes offers special problems. The difficulties are particularly great when the sample concentration is low, because the adsorption onto the surfaces with which the solutes c ome into contact may be very strong. The adsorption not only decreases the original sample concentration but also often alters the relative concentrations of the solutes, causing serious deviations from the ori ginal composition of the sample. A novel concentration method is descr ibed using a hollow fiber filled with the dilute sample solution. The technique is based on the transport of water out of the fiber through the pores in its wall and has the advantage that solute adsorption is negligible, at least when the solute concentration is not extremely lo w. The water transport can be achieved by passive or active evaporatio n or by the Donnan effect, accomplished by immersing the fiber filled with sample into a polymer solution. The method has the advantage that it permits concentration of all substances independently of their mol ecular weight. Proteins, for instance, were enriched 3000-fold in one step. By using an array of fibers and collecting all of the concentrat ed zones for a second concentration, the degree of concentration can t heoretically become 3000(2) = 9 x 10(6)-fold, provided that the limit of solubility is not exceeded. The speed of enrichment of proteins;was 14-fold per minute for a fiber with an inner diameter of 0.2 mm, leng th 280 mm, and wall thickness about 0.01 mm in the dry state (the spee d can be increased considerably by blowing air over the fiber, e.g., b y means of a fan). Simultaneously with the concentration, some purific ation of the sample can often be achieved by using a fiber with an app ropriate molecular weight cutoff value.