Fast, high-resolution (capillary) electrophoresis in buffers designed for high field strengths

Capillary electrophoresis in conventional buffers and in 50 microns capillaries permits field strengths as high as 300-500 V/cm with acceptably low thermal zone deformation. However, still higher field strengths (up to at least 2000 V/cm) can be applied without a decrease in resolution if the experiments are performed in the buffers described in this paper. Characteristic of these buffers is their low electrical conductivity and yet satisfactory buffering capacity accomplished either (i) by selecting buffer constituents of relatively high molecular weight and small net charge or (ii) by fractionation of carrier ampholytes (originally introduced for isoelectric focusing experiments) into a series of narrow pH range fractions and using these fractions as buffers, or (iii) by selecting an ampholyte with two acidic groups and one basic group (or one acidic group and two basic groups) and with a pI value close to two of its pK values. In such buffers, aromatic carboxylic acids and proteins used as model substances could be analyzed rapidly. For instance, albumin and transferrin were separated at 30,000 V (1.99 microA) in 15 cm long fused silica capillaries (50 microns ID) within 40 s and the carboxylic acids within 25 s. The resolution was similar to that obtained at standard voltage (5000 V; 0.33 microA), but the analysis time was reduced sixfold. Although not verified experimentally we also suggest the use of relatively high-molecular-weight polyoxyethylene derivatized with one acidic group (for instance, boric acid) and one basic group (an amine), both having the same pK value, which should afford both a very high buffering capacity and very low electrical conductivity (at low buffer concentrations).