Malvern Zetasizer Nano Series, User Manual

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This is a plot of the variation in average intensity versus the concentration. The
intercept of the extrapolation to zero concentration is calculated.
Minimum concentration
The minimum concentration of sample that should be used is defined by the
excess scattering over the solvent which should be a minimum of 30%, e.g. If the
solvent is toluene with a count of 150 Kcps then the lowest sample concentration
should be greater than 150 x 1.3 kcps (195Kcps). Careful sample preparation
procedures can make it possible to measure a sample with only 10% excess
scattering but this is not ideal.
Maximum concentration
The maximum concentration will be sample dependent and will be determined
by the onset of particle interactions. Typically it is best to keep the maximum
concentration to below 0.1w/v%
Preparing the sample - Zeta potential
The optical arrangement for zeta potential measurements in the Zetasizer Nano
series means that the concentration requirements are not as strict as those used for
size and molecular weight measurements.
An auto attenuator fitted inside the instrument ensures that the sample count rate
is suitable for the requirements of the detector. However if the sample is too
concentrated a low sample count rate error will be displayed. For example, for a
300nm oil in water emulsion this will be the case for concentrations higher than
0.5w/v%.
Too low a concentration will be indicated by the system setting an attenuator
index position of 11, and the generated results being variable.
In extreme cases, or where there is a bubble in the cell, a ‘low sample
concentration’ error may be displayed.
Many samples will require dilution and this procedure is absolutely critical in
determining the final value measured. For meaningful measurements the dilution
medium is crucially important. A measurement result given with no reference to
the medium in which the material is dispersed is meaningless. The zeta potential
is as dependent on the composition of the disperse phase as it is on the nature of
the particle surface.
C H A P T E R 6
Z e t a s i z e r N a n o S e r i e s
P a g e 6 . 6
M A N 0 3 1 7