Capillary isoelectric focusing (CIEF) provides excellent resolution of
proteins with the advantage that separations are carried out in a cap
illary format with on-tube detection and automated analysis. Recent ad
vances in the technique provide improved resolution, reproducibility a
nd reliability. This review summarizes improvements in sample preparat
ion, capillary selection, and focusing and zone mobilization procedure
s which have helped CIEF become a more robust analytical method. New a
pplications are reviewed, in particular the use of CIEF in analysis of
biopharmaceutical products.