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NanoPlus Operator’s Manual Zeta Potential Determination by Electrophoretic Light Scattering
Mar 2014 E-11
The amount of frequency shift

D
of scattered light is related to the mobility of particles, U:
(10)
where
q = the scattering vector, where q is 4

nsin(

/2)/


= the wavelength of the incident light
n = the refractive index of a medium

= the scattering angle

In many aqueous solutions containing an electrolyte, zeta potential can be calculated from the
Smoluchowski equation.
(11)
Where

0
and

r
are dielectric constants in vacuo and of the solvent, respectively.
Power Spectrum for Zeta Potential Measurements
Power Spectrum analysis provides an easy and direct way to obtain electrophoretic mobility
information. The instrument acquires the ACF first and then converts into power spectrum by the
Fourier transformation (Figure 7). In the distribution graph (Figure 8), the Brownian motion of the
particles is characterized by a Lorentzian peak, centered at a frequency shift that characterizes
electrophoretic mobility of the particles. If the sample is a mixture of particles of different
mobility, for example, 2, then 2 peaks can be selected for Lorentzian fit.
Figure 7. ACF and Power Spectrum of Base Measurement

D

q

2

----------

2
---

n

------

sin = cos =



0

r
---------

=