Affinity capillary electrophoresis

Analyte identification in capillary electrophoretic separation techniques

A review on applications of on-line hyphenation in capillary electrophoresis and capillary electrochromatography for the identification of migrating analytes is presented. There is an urgent need for unambiguous analyte identification by combining spectral information and observed migration times, because the parameters influencing the migration times and separation efficiencies in these separation techniques are not easily controlled, especially when real samples containing unknown interferences have to be analyzed. The spectrometric techniques covered here are ultraviolet and visible radiation (UV/Vis) absorption, fluorescence including fluorescence line-narrowing spectroscopy, Raman spectroscopy, nuclear magnetic resonance and mass spectrometry. Attention is essentially confined to literature reports in which the extra information provided by the detector is really used for identification purposes, especially in real-life samples, while the interfacing as such and analyte detectabilities in standard solutions are only briefly discussed. This article covers an extensive fraction of the literature published on this topic until the beginning of 1998.

Monoclonal antibody binding affinity determined by microchip-based capillary electrophoresis

The affinity constant of a monoclonal antibody to fluorescently labeled bovine serum albumin (BSA) was measured in diluted mouse ascites fluid using a microfluidic chip to perform affinity capillary electrophoresis. Borofloat glass-based devices could be used repeatedly with samples for many months. On-chip separations were performed in less than 60 s, and 30-60 s was required for manual sample exchange. The change in peak height for BSA with increasing BSA/anti-BSA concentration ratio was used to determine concentration changes in bound and free BSA. A Scatchard plot analysis gave an affinity constant (more exactly the intrinsic association constant) of 3.5+/-0.6 x 10(7) M(-1) for a 1:1 stoichiometric ratio. Two affinity complexes were separated. One complex was identified by the Scatchard method as having a 1:1 stoichiometric ratio. The other complex is proposed to have a stoichiometry with an excess of anti-BSA to BSA, most likely (anti-BSA)2-BSA, on the basis of a faster migration time than the 1:1 complex, a decrease in the amount of this complex with increasing [BSA], and predictions of theoretical models for multi-valent antigens. Potential applications of microchip-based devices in affinity measurements are discussed.

Affinity capillary electrophoresis: important application areas and some recent developments

Affinity capillary electrophoresis (ACE) is a broad term referring to the separation by capillary electrophoresis of substances that participate in specific or non-specific affinity interactions during electrophoresis. The interacting molecules can be found free in solution or can be immobilized to a solid support. Every ACE mode has advantages and disadvantages. Each can be used for a wide variety of applications. This paper focuses on applications that include purification and concentration of analytes present in diluted solutions or complex matrices, quantitation of analytes based on calibration curves, and estimation of binding constants from direct and derived binding curves based on quantitation of analytes or on analyte migration shifts. A more recent chemicoaffinity strategy in capillary electrophoresis/capillary electrochromatography (CE/CEC) termed molecular imprinting ('plastic antibodies') is discussed as well. Although most ACE studies are aimed at characterizing small-molecular mass analytes such as drugs, hormones, and peptides, some efforts have been pursued to characterize larger biopolymers including proteins, such as immunoglobulins. Examples of affinity interactions that have been studied are antigen-antibody, hapten-antibody, lectin-sugar, drug-protein, and enzyme-substrate complexes using ultraviolet, laser-induced fluorescence, and mass spectrometer detectors. This paper also addresses the critical issue of background electrolyte selection and quantitation of analytes. Specific examples of bioaffinity applications are presented, and the future of ACE in the biomedical field is discussed.

A heparin-binding peptide from human serum amyloid P component characterized by affinity capillary electrophoresis

Affinity capillary electrophoresis (CE) was used for a detailed characterization of the binding between heparin and a peptide isolated from the heparin-binding serum protein amyloid P component (SAP). The peptide corresponds to a tryptic fragment (T3) comprising amino acids 14-38 of SAP. By including ligands in the electrophoresis buffer various glycosaminoglycans could be screened for binding of T3 using one sample aliquot. The binding was found to be highly specific for heparin and heparin fragments down to tetramers and appeared strongest at a slightly alkaline pH while no binding could be demonstrated with heparan sulfate, chondroitin sulfate, desulfated heparin, mannose 6-phosphate and phosphotyrosine. The T3-heparin complexes were sufficiently stable to perform quantitative measurements of the binding using preequilibration of samples prior to a CE-mediated separation of bound and free T3-peptide. Plots based on quantitation of analyte peaks corresponding to free and complexed T3 yielded a dissociation constant of 1.5 microM for the interaction with heparin. The results indicate that a specific subfraction of the heparin molecules is active in binding interactions with the peptide. The affinity CE approach proved to be useful for these studies because of its sensitivity to complex formation involving charged ligands and the possibility of achieving separations under native conditions. Also advantageous is the low sample consumption and the ability to analyze unlabeled reactants in solution.