Document the measurement
It is always good practice to document your measurement so that you will
be able to identify what was measured and how it was measured. A short
sample identifier and notes can be saved with the measurement.
Measure the background
The scattering pattern from your sample is contaminated by light scattered
by impurities within the dispersant, on the windows and lenses and also
electrical “noise”. To remove this contamination a “background”
measurement is made that measures the scattering pattern with no sample
in the analyser beam. This background measurement is then subtracted
from the scattering pattern with the sample present to leave only the
information from the particles.
Add the sample and inspect the concentration
The correct amount of sample has to be passed through the laser beam to
allow a good measurement to take place. Too little sample and there will
not be enough scattered light to be detected. Too much sample and the
light scattered from an individual particle will itself be scattered by other
particles - this is known as multiple scattering.
The Mastersizer determines the correct concentration of the sample by
measuring the amount of laser light that has been lost by passing it through
the sample. This is known as the “obscuration” and is given as a percentage.
For example if 30% of the laser light is lost when it passes through the
sample it is said to have an obscuration of 30%.
Sample is added to the system until the obscuration is within an acceptable
range.
'
Note
.
The preparation of the sample before it is added to the system can be
critical. Over half of the problems encountered when measuring a
sample are caused by bad sample preparation. If your sample is sticking
together, dissolving, floating on the surface or if you have failed to get a
representative sample you will not get a correct result. Read chapter 9
for details on sample preparation.
Measure the sample
Once all the steps above are completed the scattering pattern is then
measured.
CHAPTER 3
GETTING STARTED
Page 3.5
To Next Page
Loading...
Need help?
General
