LaMotte COD Plus Colorimeter 1922-EX2 - Manual (Page 113)

INTERFERENCES: Sulfides and large amounts of iron interfere. Color and
turbidity may be removed by standardizing the instrument
with the original water sample. Since silica is a component of
glass waste and a common contaminant, it is suggested to
run a reagent blank using silica-free water. The blank value
is subtracted from the sample concentrations.
SILICA - LOW RANGE 2/3 COD PLUS TEST PROCEDURES 6/02