The first dimension in a 2-D gel electrophoresis experiment involves the separation of proteins according to their pI by isoelectric focusing (IEF).

IEF works by simultaneously applying pH and voltage gradients to a protein sample. The proteins separate as they migrate through the pH gradient in response to the applied voltage. When a protein reaches a pH value that matches its pI, its net electrical charge becomes neutral, and it stops migrating. In this way, each protein in a sample becomes "focused" according to its pI.

Bio-Rad offers a number of products for IEF — the PROTEAN IEF cell, ReadyStrip IPG strips, and other accessories — that accommodate a wide range of sample sizes and pI ranges for maximum flexibility.