20
SECTION 2, continued
2.3.3.1 Dilution Water Filtration
2.3.4 Indexing and Matching Sample Cells.
Precise measurement of multiple, low-turbidity samples requires good laboratory
techniques to achieve accuracy and good repeatability. Matched sample cells are
required to minimize the effects of optical variation among cells. Alternatively,
a single sample cell used for every measurement minimizes reading variability
caused by cell to cell imperfections. Once cell orientation in the cell holder is
established, always use the alignment indicated on the cell, regardless of
sample-cell choice (refer to Section 2.3.4.1 on page 20 and/or Section 2.3.4.2 on
page 22). Using a single cell provides better accuracy and precision than matched
cells. A Flow-Cell System provides the best accuracy and reproducibility with the
added advantage of sample pour through convenience (see SECTION 5 on
page 49).
2.3.4.1 Indexing a Single Sample Cell
Add an orientation mark to a single sample-cell as follows:
1. Attach the syringe to
the 3-way valve by gently
twisting the square end
into the syringe tip. Attach
the connector, tubing and
a 0.2 micron filter (clear
part faces syringe) as
shown. Be sure the
connections are tight.
2. Fill a beaker or
container with the waterto
be filtered. Insert the
tubing into the container.
Slowly draw the water
into the syringe by pulling
up on the syringe plunger.
3. Draw about 50 mL of
sample into the syringe.
Slowly push on the
plunger to force the water
through the filter and into
a graduated cylinder or
volumetric flask. Repeat
Steps2and3until
obtaining the desired
amount of water.
Note: Pushing water through
the filter becomes more
difficult as the filter clogs.
Discard a clogged filter and
attach a new filter when
necessary. Replacement
filters are available in
packages of 10 (Cat. No.
23238-10).
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