Will chlorine interfere with the indigo ozone method?
Chlorine interference with ozone testing.
Chlorine will not interfere with the indigo carmine, ozone method up to a concentration level of 10 mg/L chlorine. At this point the masking agent (malonic acid) will be the limiting reactant and all additional chlorine will count as a false positive. Per standard methods, addition of malonic acid can be used to mask chlorine.