Quantitative studies on the adsorption of proteins to the bare silica wall in capillary electrophoresis: III: Effects of adsorbed surfactants on quenching the interaction

The efficacy of two classes of surfactants, non-ionic and zwitterionic, in quenching the interaction of proteins with the naked silica wall in capillary electrophoresis, is evaluated. The class of non-ionic detergents is found to be rather inefficient in preventing protein binding to the fused-silica surface, since large amounts (up to 10%) are required for reducing such interactions by 90%. Conversely, zwittergents appear to be much more efficient, since, in the case of sulphobetain SB-16, 90% binding inhibition is achieved at a concentration of surfactant of only 0.3%. In this last case, it is found that the binding inhibition closely follows the values of critical micellar concentrations (CMCs) of the various surfactants, those having the lowest CMC value exhibiting the highest inhibition power. The CMC values also follow a hydrophobicity scale, suggesting that the most hydrophobic zwittergents are the ones that shield more efficiently the silica surface.