Suppression of apparent fluid flow in capillary isotachophoresis without recourse to capillary coating

This manuscript describes a new analytical methodology that allows one to stop the apparent fluid flow in uncoated fused silica capillaries. This method, which requires neither capillary coating nor buffer additive, is based on the use of a 22% polyethylene oxide gel which is placed at the anodic end of the capillary. Its high viscosity precludes its penetration into the capillary and the apparent electro-osmotic pumping effect is stopped. To avoid sample depletion in the gel, the concentration of the background electrolyte in the gel has to be at least 10-fold higher than that of the background electrolyte. This method was applied to isotachophoretic experiments performed in unmodified silica capillaries and at high alkaline pHs. The sharpness of the zone boundaries was perfectly conserved. The separation voltages recorded during the isotachophoretic processes demonstrate a very good stability of the system preventing fluctuations of the analyte migration times between runs. This approach can be virtually applied at any pH value of the background electrolyte, in the presence of organic solvents or surfactants. Using this methodology, it has been possible to detect underivatized Amyloid-β peptide 1-40, one of the potential Alzheimer's disease biomarkers, at lower concentrations than ever previously achieved using UV detection.