Reducing Sample Complexity in Proteomics<br>by Chromatofocusing with Simple Buffer Mixtures

Chromatofocusing has many potential applications in the field of proteomics, such as for the isolation and removal of major sample components to facilitate the analysis of low-abundance components, and for sample prefractionation prior to a subsequent separation using SDS-PAGE, narrow-pI -range 2D-PAGE, or additional chromatography steps. However, the chromatofocusing techniques that are most commonly used employ propriety polyampholyte elution buffers and highly specialized column packings, both of which limit the use of chromatofocusing in practice. To expand the range of application for this technique, this chapter considers chromatofocusing methods which employ common ion-exchange column packings and elution buffers which are simple mixtures of readily available buffering species. Of particular interest is the use of chromatofocusing with a multistep pH gradient for the fractionation of protein mixtures into narrow-pI -range fractions. The cross-contamination characteristics of these fractions using SDS-PAGE are also assessed.