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SECTION 2,
continued
2.6.3.2
Matching Sample Cells
1.
Add portions of the high-
quality dilution water to
multiple cells that are clean,
and coated with silicone oil.
Note: For more information,
see:
Section 2.5.1 Cleaning
Sample Cells
Section 2.6.1 Applying
Silicone Oil
Section 2.6.2 Preparing
Dilution Water.
2.6.4 Removing Air Bubbles (Degassing)
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Index match (orientation) multiple cells using the following procedure:
2.
Make sure the filter is in
place. Insert the first cell
into the instrument. Rotate
the cell slightly until the
lowest reading is found.
Note the cell orientation,
record the reading, and add
an index mark to the
marking band of the cell.
Remove air or other entrained gases prior to measurement. Degassing is
recommended (even if no bubbles are visible). Four methods are commonly used
for degassing:
•
Application of a partial vacuum
•
Addition of a surfactant
•
Use of an ultrasonic bath
•
Application of heat
In some cases more than one method may be necessary for effective bubble
removal (e.g., some severe conditions may require combining use of heat with an
ultrasonic bath). Use care with these techniques; sample turbidity can be altered if
these methods are misused.
3.
Insert the second cell
into the instrument, close the
lid, and note the value.
Rotate the cell
1
approximately
/
of a turn
8
and observe the reading.
1
Repeat
/
-turn rotations
8
until the reading matches the
first cell reading within
±
. Add a permanent
0.01 NTU
orientation mark to the
marking band of the second
cell. Repeat this procedure
to match other cells.
Note: It may not be possible to
match all cells due to variability
in glass.
26
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