Separating Proteins by pI - Values — Can 2 D LC Replace 2 D GE ?

The requirements of liquid chromatography (LC) separation systems to separate proteins are often different from those of small molecules as the inherent properties of proteins can result in loss by adsorption, precipitation at zero charge or broad and asymmetric peaks in liquid chromatography. This article looks at the specific separation problems of proteins; the advantages and disadvantages of gel electrophoresis compared with alternative techniques; the potential of pI separations by pH gradients rather than by isoelectric focusing; and describes a two-dimensional liquid chromatography technique that uses pI separation in the first dimension and reversed-phase separation in the second dimension.