LaMotte COD Plus Colorimeter 1922-EX2 - Manual (Page 17)

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INTERFERENCES
LaMotte reagent systems are designed to minimize most common interferences.
Each individual test instruction discusses interferences unique to that test. Be
aware of possible interferences in the water being tested.
The reagent systems also contain buffers to adjust the water sample to the ideal
pH for the reaction. It is possible that the buffer capacity of the water sample
may exceed the buffer capacity of the reagent system and the ideal pH will not
be obtained. If this is suspected, measure the pH of a reacted distilled water
reagent blank using a pH meter. This is the ideal pH for the test. Measure the
pH of a reacted water sample using the pH meter. If the pH is significantly
different from the ideal value, the pH of the sample should be adjusted before
testing.
Interferences due to high concentration of the substance being tested, can be
overcome by sample dilution (p. 16).
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STRAY LIGHT INTERFERENCE
When scanning samples in 16 mm tubes, such as COD, the sample chamber lid
can not be closed. The COD adapter minimizes stray light. To further reduce
stray light interference, do not scan sample in direct sunlight.
COD PLUS COLORIMETER 6/02 17