Capillary electrophoresis of peptides and proteins in isoelectric buffers: an update

Capillary electrophoresis in acidic, isoelectric buffers is a novel methodology allowing fast protein and peptide analysis in uncoated capillaries. Due to the low pH adopted and to the use of dynamic coating with cellulose derivatives, silanol ionization is essentially suppressed and little interaction of macromolecules with the untreated wall occurs. In addition, due to the low conductivity of quasi-stationary, isoelectric buffers, high-voltage gradients can be applied (up to 800 V/cm) permitting fast peptide analysis with a high resolving power due to minimal diffusional peak spreading. Four such buffers are here described: cysteic acid (Cys-A, pI 1.85), iminodiacetic acid (IDA, pI 2.23), aspartic acid (Asp, pI 2.77) and glutamic acid (Glu, pI 3.22). A number of applications are reported, ranging from food analysis to the study of folding/unfolding transitions of proteins.