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.
