As is evident from the pH titration, the isoelectric poi nt of the wall is near pH = 4.5. A typical pH dependence of the wall zeta potential for the DTS1060 disposable capillary cells used with the Zetasizer Nano system is shown in the figure below. In general, high pH values induce a highly negative charge on the wall, while high buffer concentrations tend to screen the e ffective charge of the wall. The wall zeta potential is influenced strongly by solvent conditions. The Zetasizer Nano system takes advantage of this time difference, by using the patented M3 measurement technique, wherein the mean mobility is measured in the absence of electroosmosis during the fast field reversal (FFR) portion of the measurement, and the zeta potential distribution is measured during the slow field reversal (SFR) portion of the measurement and then corrected for electroosmotic effects using the FFR results. Fortunately, the time scale for the establishment of electroosmotic effects in a capillary cell is significantly longer than the time scale for the establishment and measurement of the electrophoretic mobility of a charged macromolecule. This solvent motion or flow is called electroosmosis, and will contribute to the apparent mobility of charged particles when measured in the presence of electroosmosis. When an external electric field is applied across the capillary cell the solvated ions near the cell surface will move under its influence, drag ging solvent along in the process. The wall zeta potential is a measure of the electric potential at the wall slipping plane (Figure 1), located within the diffuse layer.įigure 1: Schematic describing the double layer established near a charged surface, along with the location of the slipping plane where the wall zeta potential is measured. As a result of this charge, a layer of positive ly charged cations builds up n ear the surface to maintain charge balance, creating a diffuse layer of ions near the cell surface in the process. Under most common experimental conditions, the capillary wall of the DTS1060 disposable zeta potential cell used in the Zetasizer Nano system is negatively charged. For electrophoretic light scattering (ELS) instruments utilizing capillary cells, electroosmosis will likely be present, due to the presence of surface char g e on the inside of the capillary wall. What_is_the_wall_zeta_potential_ What is the wall zeta potential?Įlectroosmosis is the movement of liquid relative to a stationary charged surface under the influence of an applied field.