Quadrature phase analysis light scattering for electrophoresis and zeta potential measurements

A device for measuring displacement and direction of displacement of particles undergoing electrophoresis in an electrophoresis sample chamber, comprising:

• an optical quadrature interferometer having an electrophoresis sample chamber, the electrophoresis sample chamber and the particles being positioned in a path of a main beam to produce a scattered light, the optical quadrature interferometer being configured to perform quadrature phase analysis light scattering on the particles by using the scattered light to generate a quadrature signal comprising characteristics related to the displacement and direction of displacement of the particles, the particles being urged by an alternating electric signal applied to electrodes of the sample chamber, and an analyzer comprising signal processing means for acquiring a data record of the quadrature signal, evaluating a function of the data record, and determining a central value of the function substantially at the frequency of the alternating electric signal,
• whereby the central value is used to determine a displacement and a direction of displacement of the particles, thereby aiding the determination of magnitude and polarity of electrophoretic mobility and zeta potential of the particles.