the light scattered from the particles can be obtained. The
measurement of background scattering is sometimes called a "ZSCAT".
The name comes from the fact that the measurement is obtained using
water with zero "scatterers" or particles.
It is very important that clean and bubble free water is used. The water
can be fresh or salt water. For most applications, it has been found
that steam-distilled water is sufficient. Steam-distilled water is typically
available in one-gallon containers. We have found that this distilled
water tends to be a bit cleaner than typical bottled or packaged water.
We buy steam-distilled drinking water and filter it through a 0.2µm filter.
A small volume horizontal chamber has been provided for submerging
the optics while acquiring a background. It is inserted between the
windows of the optics. The instrument should be placed horizontally on
the supplied white plastic supports. However, Plastic bags, Tupperware
or clean containers of any kind can be used to acquire a background.
The instrument’s optics end can be submerged in them vertically, as
long as the optics are completely submerged and there is no blockage
of the windows by bubbles or other objects.
Because the area surrounding the windows is submerged, it is
important to thoroughly clean and rinse this part of the instrument
before acquiring a background.
Toothbrush, liquid soap and water works well for cleaning the optical
end of the instrument; do not use abrasive powders, they will scratch
optics and destroy instrument performance.
The low concentration limit of LISST-200X is very sensitive to the
quality of the background scatter file. For this reason, when working in
low concentration water, it is very important that a good background file
be obtained with very clean water. As particle concentrations increase,
the relative signal-to-background noise ratio also increases, thus
reducing the importance of the background. However, a background
should always be collected before an experiment.
Another consideration when acquiring a background is "outgassing"
causing small bubbles to form on the instrument and windows.
Bubbles on the windows will greatly modify the scattering pattern,
rendering the background useless. Be sure to remove any bubbles
from the windows before acquiring a background. Use a squirt bottle or
pipette to blow the bubbles off the window.
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