Laser Doppler Velocimetry
Laser Doppler Velocimetry (LDV) is a method for measuring the speed of small particles. When particles are suspended in a fluid in the presence of a known electric field, a velocity measurement is a measure of the mobility of the particles. For the majority of samples, the mobility is directly related to the zeta potential of the particles, a parameter of concern to those working in a range of fields from paper manufacturing to waste water treatment to pharmaceutical development. LDV is analogous to speed measurements of cars made by radar. Small particles suspended in fluid are illuminated by a laser beam and the light scattered to various angles is compared to light in a reference beam to determine the doppler shift of the scattered light. The doppler shift of the light depends on the speed of the particles and the angle of measurement.
By making four independent, simultaneous measurements at four angles, the COULTER® DELSA 440SX is the only zeta potential instrument which provides validation of mobility peaks, and which can be used to determine the relative sizes of particles at different mobilities. The DELSA 440SX is a high resolution instrument with the flexibility to optimize measurements for different samples, and to measure samples over a wide range of conductivities and particle mobilities. Size distributions can also be obtained with the DELSA 440SX, using the same cell and sample as used for mobility measurements.
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