For the Zetasizer Nano Z, ZS or ZS90 instrument, the maximum size specification (diameter) for zeta potential measurements is 100µm. This technical note contains details of the experimental procedures and results obtained from measurements of a NIST traceable polystyrene latex standard as demonstration of this maximum size specification for zeta potential measurements.
A drop of the 100µm polystyrene latex was added to 1ml of the 13% w/v sucrose solution and thoroughly mixed to ensure proper dispersion. This dispersant was chosen to match the density of the latex, which has a density of 1.05, in order to do a number of measurements before the particles sedimented from the measurement volume.
The measurements were taken at 25°C using a viscosity of 1.40mPa.s.
The zeta potential distributions obtained from 3 repeat measurements of the 100µm polystyrene latex dispersion are shown in figure 1.
Table 1 is a summary of the 3 repeat measurements and shows the zeta potential mean (in mV) and the zeta potential deviation (the standard deviation of the peak in mV). The repeatability of the results confirms that successful zeta potential measurements of 100µm sized particles can be made on a Zetasizer Nano instrument.
Zeta Potential Mean (mV)
Zeta Potential Deviation (mV)
Figure 2 shows the phase plots obtained from the 3 repeat measurements which were used to calculate the mean of the three zeta potential distributions. These highlight the excellent quality of the data obtained.
It is often thought that electrophoretic mobility and hence zeta potential is a function of size, and hence sedimentation, will affect the result. Theory suggests that the zeta potential of particles is independent of the particle size. Technical note MRK112 demonstrates that zeta potential can be measured while the particles are sedimenting, and that the results are stable.
The results reported in this technical note confirm that the maximum size capability (diameter) for zeta potential measurements with the Zetasizer Nano Z, ZS or ZS90 is 100µm.