LaMotte 1200 Colorimeter - Manual (Page 13)

INTERFERENCES
LaMotte reagent systems are designed to minimize most common interferences.
Each individual test 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 (see page 12).
STRAY LIGHT INTERFERENCE
Stray light interference can be minimized by always zeroing the meter and
reading a sample with the lid closed. Turbidimetric determinations (i.e. sulfate)
are most likely to exhibit a stray light interference. Colorimetric tests are less
likely to have this problem unless the samples are turbid. If sample turbidity is
causing a stray light interference, filtration may be needed.
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