Environmental Engineering Reference
In-Depth Information
to visualize particles in any solvent type, the suspending medium must be
sufficiently nonabsorbing, nonindex matching and gas free.
(b) Particle Size Range Applicable. The NanoSight system allows particles as small
as 10-20 nm and particles as large as a micron to be seen to be visualized
(depending on particle and solvent type). The large particles (
>
μ
m) will scatter
significant amounts of light and may mask the presence of smaller particles if
present at too high a concentration. The very large particle aggregates (
1
>
m)
may affect image quality or might block the sample inlet/outlet ports and should
be removed by filtration or centrifugation before the sample is analyzed.
(c) Particle concentration. For particles to be resolved on an individual basis, it is
necessary for the sample to be diluted to a particle number concentration of
<
10
μ
10 10 per ml though this limit will vary with sample type. It is best to adjust
sample concentration until a clear image is obtained of a population of at least
100 particles in the scattering volume. The laser beam is focused, on manu-
facture, to generate a beam waist of approx. 100
μ
m widths of which a length
m is observed.
(d) Dilution. The sample must be diluted to a number concentration of between
10 6 and 10 10 particles per milliliter (depending on particle type) and not
contain particles larger than 10
of beam of between 100
μ
m diameter. Such particles will degrade
image quality and may sediment in the sample chamber necessitating frequent
cleaning of the optical surfaces. Should the sample require dispersion before
analysis, gentle agitation can be used, although the introduction of bubbles
into the sample will degrade image quality (bubbles are very effective light
scattering centers). Small quantities of dispersant, or a suitable detergent, may
be employed, but formation of foam should be avoided.
(e) Physical removal of large particles. Physical removal of large particles can be
performed simply by filtration or centrifugation of the sample or allowing the
sample to settle over a suitable time period.
(f) Dispersion and agglomeration. Choosing the correct dispersing agent is central
to the formation of a stable dispersion, and the identification and selection of a
suitable dispersant requires a significant understanding of the sample and its
interaction with its suspending solvent. The agent should not interfere with the
measurement itself, it should be able to contact the primary particle without
causing it to dissolve and it should prevent aggregation of the primary particle.
In the absence of an established dispersion protocol for any given sample type,
empirical methods are the only way by which optimum dispersion protocols
can be arrived at.
μ
13.3.4 LM10 Usage
Use NanoSight LM is done by respecting several stages.
(a) Assembling the LM sample unit
The LM sample unit can be assembled as follows: switch off unit and remove
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