IEF is well established as an exellent technique for the analysis of proteins, such as enzymes, hormones or other biologically active proteins.

 A pH gradient is formed in a supporting medium by subjecting carrier ampholytes to an electric field. When a protein is placed within the pH-gradient, it migrates under the influence of the current to its specific isoelectric point (pI), stays at this position and can be visualized as a characteristic banding pattern.

Isoelectric focusing (IEF) differs from many other electrophoresis techniques in that the protein is actively concentrated, or focused, at its isoelectric point: it is possible to resolve two proteins with a difference in pI of only 0.01 pH units.