Dilution Procedure; Preparation Of Turbidity-Free Water - LaMotte 2020t/i Mode D'emploi

ENTER
14. Press
and scan the sample. The screen will
display Reading for about 1 second.
The result will appear on the screen.
"Overrange" will be displayed if
the reading is out of range. Dilute
the sample or select a mode that
is appropriate for the range of the
sample.
NOTE: The meter will remember the last scanned blank reading. It is not necessary to scan
a blank each time the test is performed. To use the previous blank reading, instead of
scanning a new one, scroll to Scan Sample and proceed. For the most accurate results, the
meter should be blanked before each test and the same tube should be used for the blank
and the reacted sample.
 DILUTION PROCEDURES
If a sample is encountered that is more than 2000 NTU or FNU, a careful dilution with
0 NTU/FNU or very low turbidity water will bring the sample into an acceptable range.
However, there is no guarantee that halving the concentration will exactly halve the NTU or
FNU value. Particulates often react in an unpredictable manner when diluted.
Turbidity-Free Water
The defi nition of low turbidity and turbidity-free water has changed as fi lter technology
has changed and nephelometric instruments have become more sensitive. At one time
turbidity-free water was defi ned as water that had passed through a 0.6 micron fi lter.
Now 0.1 micron fi lters are available and higher purity water is possible. Water that has
been passed through a 0.1 micron fi lter could be considered particle free and therefore
turbidity free, 0 NTU water. Turbidity is caused by scattered light. Therefore, low turbidity
water is water without any particles that scatter a measurable amount of light. But water
that passed through a 0.1 micron fi lter may still have detectable light scatter with modern
instruments. This light scattering can be the result of dissolved molecules or sub-micron
sized particles that can not be fi ltered out of the water. Because there may still be a small
amount of scattered light from dissolved molecules, high purity water is often called low
turbidity water and assigned a value of 0.01 or 0.02 NTU. However, because this water is
used as a baseline to compare to sample water, the diff erence between the sample and the
low turbidity or turbidity-free water will be the same whether it is called 0.00 NTU or 0.02
NTU. For design simplicity the 2020t/i uses the term turbidity-free water and the value of
0.00 NTU.
 PREPARATION OF TURBIDITY-FREE WATER
A 0 NTU/FNU Standard (Code 1480) is included with the meter. Accessories are available
for preparing turbidity-free water for blanking the meter and dilution of high turbidity
samples.
The preparation of turbidity-free water requires careful technique. Introduction of
foreign matter will aff ect the turbidity reading. A fi ltering device with a special membrane
fi lter is used to prepare turbidity-free water. The fi lter, fi lter holder and syringe must be
conditioned by forcing at least two syringes full of deionized water through the fi ltering
apparatus to remove foreign matter. The fi rst and second rinses should be discarded.
Turbidity-free water as prepared with the following procedure may be stored in the dark
at room temperature in a clean glass bottle with a screw cap and used as required. The
storage container should be rinsed thoroughly with fi ltered deionized water before fi lling.
The water should be periodically inspected for foreign matter in bright light.
to select Scan Sample
Turbidity WB (N)
0.99
NTU
Scan Blank
Scan Sample
12:00:00 001/500
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