Environmental Engineering Reference
In-Depth Information
13.3.2.2 Size vs. Fluorescence
The ability of NTA to simultaneously measure particle size and particle scattering
intensity and with fluorescence allows heterogeneous particle mixtures to be
resolved. Particle concentration can be estimated directly, the particle size distri-
bution profile obtained by NTA being a direct number/frequency distribution. The
method allows fluorescence measurement for specific particle types to be charac-
terized (sized, counted) in complex mixtures through, for instance, the use of
fluorescently labeled antibodies and other probes.
The accuracy of results obtained by the NANOSIGHT NTA Nanoparticle
Tracking system is dependent on a number of factors, primarily particle concen-
tration analyzed, the length of time over which the sample is analyzed, and the size
of the particles present. While the sample chamber is approximately 250
lin
volume, the section of the laser beam visualized (the scattering volume) is very
small (a cylinder approx. 70
μ
m length). Accordingly, for a
statistically significant number of particles to be present on the beam, sample
concentrations should have values between 105 and 1010 particles/ml. Higher
concentrations (e.g., 1010/ml) with a measurement accuracy of a shorter analysis
(see Fig.
13.7
). Similarly, observing a sample for 10 s (300 sequential images at
30 fps) will result in better statistical accuracy than an analysis of 1 s. Table
13.1
shows the effects of increasing particle concentration and analysis time for a
suspension of ash from the incinerator.
μ
m diameter
80
μ
13.3.3 Sample Preparation and Dispersion
The NanoSight device as a particle sizing system based on the scattering of light
measures all particles visible in the sample and each separate light scattering center
is seen as an individual particle, whether or not it is made up of a number of small
particles, i.e., is an aggregate and agglomerate of primary particles. Should the user
be interested in the detection and analysis of such aggregates, sample preparation is
restricted simply to effecting a suitable dilution for analysis.
Should the number of aggregates will be low (compared to the number of
primary particles within the sample population) the unique capability of the
NanoSight technique to simultaneously analyze each and every particle on an
individual basis means the presence of low numbers of aggregates will not interfere
with the analysis of the bulk of primary particles [
17
].
(a) Suspending solvent. The presence of aggregates (and agglomerates or flocks)
is undesirable in so far as they are present at such a high number that they
interfere with or dominate the analysis and result. Aggregates can be dispersed
in a number of ways using physical processes such as ultrasonication or the
application of high shear forces. The standard LM viewing unit is configured
to operate optimally with water-based samples. While the device can be used
