Interferences; Stray Light Interference - LaMotte SMART Colorimeter Operator's Manual

If the above glassware is not available, dilutions can be made with the
colorimeter tube. Fill the colorimeter tube to the 10 mL line with the
sample then transfer it to another container. Add 10 mL volumes of
demineralized water to the container and mix. Transfer back 10 mL of the
diluted sample to the colorimeter tube and follow the test procedure.
Continue diluting and testing until a reading, which is in the
concentration range for the test, is obtained. Be sure to multiply the
concentration found by the dilution factor (the number of total 10 mL
volumes used).
Example:
10 mL of sample is diluted with three 10 mL volumes of demineralized
water; the dilution factor is four.

INTERFERENCES

LaMotte reagents 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 14).

STRAY LIGHT INTERFERENCE

Normal indoor lighting causes no interference with the SMART
Colorimeter. Testing in bright sunlight may result in interferences due to
stray light. This interference can be eliminated by covering the
colorimeter chamber with the black cap when zeroing the meter and
reading samples. Turbidimetric determinations (i.e. sulfate, potassium,
cyanuric acid and turbidity) are most likely to exhibit a stray light
interference. Always check for stray light interferences when you do
turbidimetric determinations. Colorimetric tests are less likely to have
this problem.
SMART COLORIMETER 15