Electrophoresis Of pH-Regulated Particles In The Presence Of Multiple Ionic Species

An electrophoresis model taking account of the pH-regulated nature of particles, and the presence of multiple ionic species is proposed for arbitrary surface potential and double layer thickness. The estimated zeta potential is compared with those estimated from conventional formulas usually adopted by conventional zeta potential instrumentation. Using Fe3O4 nanoparticles in NaCl solution with pH adjusted by HCl and NaOH as an example, we show that these formulas might yield appreciable deviations. For example, at pH 9, the deviation is one the order -25 mV. With the surface charge density measured by titration and the zeta potential by electrophoresis, the true surface potential is estimated through a triple-layer model.