Environmental Engineering Reference
In-Depth Information
variation of the Stokes-Einstein equation (Eq.
13.1
)[
16
], where
K
B
is Boltzmann
s
'
constant,
T
the temperature, and
ʷ
the viscosity.
2
4
¼
ðÞ
x
;
y
TK
B
3
D
¼
ð
13
:
1
Þ
ˀʷ
d
The range of particle sizes which can be analyzed by NTA depends on the
particle type. The lower size limit is defined by the particle size and particle
refractive index. For very high particles such as colloidal gold, accurate determi-
nation of size can be achieved down to 10 nm diameter. For lower refractive index
particles, such as those of biological origin, the smallest detectable size might only
be between 25 and 35 nm. This minimum size limit allows, however, the analysis of
most types of virus [
13
].
In NTA method, there are some factors and parameters which can seriously
affect the accuracy of final particle size result, for example, sample concentration,
camera parameters, and analysis parameters setting. Therefore setting and selecting
those parameters are much important for obtaining accurate and reliable results.
13.3.2 Parameters Measurements
Capabilities of NTA measurements consist of direct and live view of particles in
suspension, particle-by-particle, high-resolution particle sizing, especially applica-
ble to polydisperse systems, measurement of concentration and particle count,
scattering intensity distribution, evidence of nonsphericity and of aspect ratio,
sizing down to 10 nm, material dependent, number vs. intensity vs. size is provided
for each particle size class, particle-by-particle measurement of electrophoretic
mobility, and subsequent calculation of zeta potential.
The direct observation of particle motion and scattering behavior provides
information beyond particle size. These real-time observations validate the reported
particle size distributions and provide instant insight into polydispersity and the
state of aggregation. Measurements take just minutes, allowing being quantified
time-based changes and aggregation kinetics.
13.3.2.1 Size vs. Intensity
The benefit of NTA which are able to simultaneously measure two independent
parameters such as particle scattering intensity and particle diameter (from dynamic
behavior) is valuable in resolving mixtures of particle. The small differences in
particle size within a population can be resolved with far higher accuracy than
would be achieved by other ensemble light scattering techniques. Accordingly, by
gating on size and light scatter it is possible to obtain reproducible counts and
