[1] The three samples are mixed and loaded onto IEF (isoelectric focusing chromatography) for first dimension and the strip is transferred to a SDS PAGE.
This technique is used to see changes in protein abundance (for example, between a sample of a healthy person and a sample of a person with disease), post-translational modifications, truncations and any modification that might change the size or isoelectric point of proteins.
[citation needed] It overcomes limitations in traditional 2D electrophoresis that are due to inter-gel variation.
Since the proteins from the different sample types (e.g. healthy/diseased, virulent/non-virulent) are run on the same gel they can be directly compared.
Since the amounts of each protein in the internal standard is known to be the same in every gel, this method reduces inter-gel variation.