On-line sample preconcentration in capillary electrophoresis, focused on the determination of proteins and peptides

This overview highlights the possibilities of on- or in-line preconcentrati on procedures in combination with a CZE separation, focused on the determin ation of peptides and proteins. The discussed methods, including sample sta cking, field-amplified injection, isotachophoresis, solid phase extraction, membrane preconcentration, electroextraction, supported liquid membranes, hollow fibers, immunoaffinity, and molecularly imprinted polymers technolog y preconcentration are categorized in electrophoresis-based and chromatogra phy-based preconcentration. The chromatography-based preconcentration is su bdivided in low-specificity and high-specificity methods. A number of preco ncentration methods are available, however, this paper demonstrates that va rious compounds in different media (aqueous solutions, urine, and plasma) r equire different preconcentration systems. The preconcentration techniques of first choice in general seem to be solid-phase extraction and membrane p reconcentration, because of their high concentration ability, multiapplicab ility, relative simplicity and clean-up capability. For the future, hollow fibers seem to hold a great potential as preconcentration technique, yieldi ng high concentration factors, using simple designs. New techniques, such a s hollow fibers, molecularly imprinted polymers technology and supported li quid membranes may have the potential to supersede the conventional pre-con centration techniques in some cases. The larger the arsenal of preconcentra tion techniques becomes, the more efficiently peptides and proteins may be analyzed in the future. These techniques, in some cases, require pre-cleanu p procedures, to ensure the purity of the samples to concentrate.