The frequency plot shows the frequency spectrum obtained from the slow field reversal (SFR) part of General Purpose measurement using a Fourier transform analysis. The frequency spectrum is used to determine the electrophoretic mobility distribution and the subsequent distribution of zeta potentials. Figure 1 shows a typical frequency plot obtained from a good electrophoretic light scattering measurement. Conversely, Figure 2 is an example of a noisy frequency distribution plot.
Figure 1: Typical frequency distribution plot of good quality obtained from a General Purpose measurement
Figure 2: Typical frequency distribution plot of poor quality obtained from a General Purpose measurement
Several factors may be responsible for poor distribution data in the frequency plot. Firstly, the sample concentration may be inappropriate. If the sample concentration is too low, insufficient scattering may have been detected, resulting in poor signal to noise ratio. In a like sense, if the sample is too turbid or too concentrated, attenuation of the laser beam will result in poor signal quality.
If the sample has a high conductivity, the application of the field during the SFR part of the General Purpose measurement may cause sample and/or electrode degradation. It is advisable to use the Monomodal measurement protocol for samples with conductivities greater than 10mS/cm. In the Monomodal measurement protocol, only the fast field reversal (FFR) measurement is collected. It should be noted however, that only a mean zeta potential is obtained with the Monomodal measurement as no distribution analysis is performed. Hence there will be no frequency plot when only the FFR measurement is utilized.
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