LaMotte 1200 Colorimeter - Manual (Page 11)

The 1200 Colorimeter has been specially calibrated to read test results directly in
parts per million (ppm) of the test factor. The sensitivity of the response has been
maximized by using a specific, complementary light source for each test.
REAGENT BLANK
Some tests will provide greater accuracy if a reagent blank is determined, to
compensate for any color or turbidity resulting from the reagents themselves. A
reagent blank is performed by running the test procedure on 10 mL of
demineralized water. Use sample water to zero the meter. Insert the reagent blank
in the colorimeter chamber and select
READ. Note result of reagent blank.
Perform the tests on the unknown as described. Subtract results of
reagent blank from all subsequent test results.
COLORIMETER TUBES
The handling of the colorimeter tubes is of utmost importance. Scratches,
fingerprints and water droplets on the tube or inside the light chamber can cause
stray light interference leading to inaccurate results. It is imperative that the
tubes and light chamber be clean and dry. The glassware must be clean and
defect-free. Scratches and abrasions will permanently affect the accuracy of the
readings. Tubes can be acid washed periodically. After a tube has been filled and
capped, it should be held by the cap and the outside surface should be wiped with
a clean, lint-free absorbent cloth until it is dry and smudge-free. Handling the
tube only by the cap will avoid problems from fingerprints. Always set the clean
tube aside on a clean surface that will not contaminate the tube.
Variability in the geometry and quality of the glassware is the predominate cause
of variability in results. Orientation of the tube in the chamber will greatly affect
the test results. To obtain the most accurate results, the tubes must be positioned
so that the index line on the tube is aligned with the arrow-shaped index mark
t
molded into the housing in front of the light chamber. This will ensure that the
most accurate results are obtained.
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