The state of the art of dynamic coatings

The present review highlights the mechanisms of action and efficiency of three major classes of dynamic coatings so far adopted in capillary electrophoresis: (i) amines to oligo-amines, (ii) neutral synthetic and natural polymers, and (iii) neutral and zwitter-ionic surfactants. Their merits and efficacy have been explored in depth via a novel quantitation technique consisting of eluting, by frontal analysis, any adsorbed proteinaceous material, which can then be correctly quantified as a peak as it moves in front of the detector window. This is achieved by loading sodium dodecyl sulfate (SDS) micelles onto the cathodic side and migrating them electrophoretically into the capillary lumen, where they efficiently sweep any adsorbed polypeptide material. It is found that a common trend, for all quenchers, is linked to a hydrophobicity scale: the more hydrophobic the inhibitor, the better it minimizes potential interactions of macromolecules with the wall. This seems to be true for all the classes of dynamic modifiers tested. Finally, we describe a novel, dynamic to static quencher: it is a quaternary piperazine, bearing a reactive iodine atom at the end of a butyl tail (N(methyl-N-omega-iodo-butyl),N'-methyl piperazine). This molecule first binds to the wall, at alkaline pH values, via ionic and hydrogen bonds. Once docked onto the wall, the reactive tail forms a covalent link with the silica surface, to which it then remains permanently affixed.