Electrophoretic light scattering
With electrophoretic light scattering, oscillating electric field performs this function.
Sample dilution is often necessary to eliminate multiple scattering of the incident laser beam and/or particle interactions.
Those cross inside the electrophresis cell at a fixed angle to produce a fringe pattern.
Oka et al. developed an ELS instrument of heterodyne-type optics[3] that is now available commercially.
If the frequencies of the intersecting laser beams are the same then it is not possible to resolve the direction of the motion of the migrating particles.
Phase-analysis light scattering (PALS) is a method for evaluating zeta potential, in which the rate of phase change of the interference between light scattered by the sample and the modulated reference beam is analyzed.
This rate is compared with a mathematically generated sine wave predetermined by the modulator frequency.
[4] The application of large fields, which can lead to sample heating and breakdown of the colloids is no longer required.
[5] The frequency of light scattered by particles undergoing electrophoresis is shifted by the amount of the Doppler effect,
The Doppler shift of frequency and the decay constant are dependent on the geometry of the optical system and are expressed respectively by the equations.
is define by the equation Finally, the relation between the Doppler shift frequency and mobility is given for the case of the optical configuration of Fig.
Figure 4 shows two examples of heterodyne autocorrelation functions of scattered light from sodium polystyrene sulfate solution (NaPSS; MW 400,000; 4 mg/mL in 10 mM NaCl).
4b includes additionally the contribution from the frequency changes of light scattered by PSS molecules under an electrical field of 40 V/cm.
Figure 5 shows heterodyne power spectra obtained by Fourier transform of the autocorrelation functions shown in Fig.
Figure 6 shows plots of Doppler shift frequencies measured at various cell depth and electric field strengths, where a sample is the NaPSS solution.
These parabolic curves are called profiles of electro-osmotic flow and indicate that the velocity of the particles changed at different depth.
Since the electrophoresis chamber is a closed system, backward flow is produced at the center of the cell.
Electrophoretic mobility analysis has been studied by Mori and Okamoto [16], who have taken into account the effect of electro-osmotic flow at the side wall.
where The parabolic curve of frequency shift caused by electro-osmotic flow shown in Fig.
The frequency shift caused only by the electrophoresis of particles is equal to the apparent mobility at the stationary layer.
The velocity of the electrophoretic migration thus obtained is proportional to the electric field as shown in Fig.
Electrophoretic light scattering (ELS) is primarily used for characterizing the surface charges of colloidal particles like macromolecules or synthetic polymers (ex.
In addition to information about surface charges, ELS can also measure the particle size of proteins[7] and determine the zeta potential distribution.
[8] The width of a Doppler shifted spectrum of light that is scattered from a solution of macromolecules is proportional to the diffusion coefficient.
[10] From studies that have applied this method to poly (L-lysine), ELS is believed to monitor fluctuation mobilities in the presence of solvents with varying salt concentrations.
[11] It has also been shown that electrophoretic mobility data can be converted to zeta potential values, which enables the determination of the isoelectric point of proteins and the number of electrokinetic charges on the surface.
The technique can be extended to measure electrophoretic mobilities of large bacteria molecules at low ionic strengths.
[15] ELS has been used to characterize the polydispersity, nanodispersity, and stability of single-walled carbon nanotubes in an aqueous environment with surfactants.
[citation needed] The technique can be used in combination with dynamic light scattering to measure these properties of nanotubes in many different solvents.
"Homodyne Electrophoretic Light Scattering of Polystyrene Spheres by Laser Cross-Beam Intensity Correlation".
