LaMotte COD Plus Colorimeter 1922-EX2 - Manual (Page 65)

INTERFERENCES: Volatile organic compounds are not oxidized to the extent
that they are in the vapor above the digestion solution.
Therefore, they do not contribute to the COD reading.
Contains mercury sulfate to prevent interference from
chloride. Nitrite gives a positive interference of 1.1 ppm O
2
per ppm NO
2
–N, which is insignificant unless nitrite
concentrations are very high. Other reduced inorganic
compounds are stoichiometrically oxidized, causing a
positive interference. Corrections can be made for these
compounds based upon their stoichiometry and
concentrations.
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 - HIGH RANGE 2/4 COD PLUS TEST PROCEDURES 2/04