Ionic concentration- and pH-dependent electrophoretic mobility as studied by single colloid electrophoresis

I Semenov, P Papadopoulos, G Stober and F Kremer

Optical tweezers are employed to measure separately the complex electrophoretic mobility of a single colloid and the complex electroosmotic response of the surrounding medium in a specially designed microfluidic cell. Using the very same colloid both quantities are determined in dependence on the concentration of the aqueous salt solution (10 − 5–10 − 1 mol l − 1), the valence of the ions (K + , Ca2 + ) and the pH (2.5–8.5). A pronounced effect is observed for all these examined parameters. The dependence on ion concentration agrees qualitatively—for the monovalent case—with the predictions of the standard electrokinetic model.

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