Is it possible to eliminate the interference of oxidized manganese and oxidized chromium from the chlorine DPD chemistry?

Document ID

Document ID TE206

Version

Version 4.0

Status

Status Published

Published Date

Published Date 09/27/2018
Question
Is it possible to eliminate the interference of oxidized manganese and oxidized chromium from the chlorine DPD chemistry?
Summary
Interferences to DPD chemistry
Answer
There is not a way to eliminate the interference of oxidized manganese and oxidized chromium, but tests can be done to compensate for the effects of oxidized manganese and chromium. The chlorine DPD methods describe the compensation steps in the interference section of the method.

1. Adjust pH to 6 to 7 as described in procedure
2.  Add 3 drops of potassium iodide, 30 g/L, to 25 ml sample
3. Mix and wait 1 minute. (This combines with the total chlorine to form iodine).
4. Add 3 drops of sodium arsenite, 5 g/L, and mix. (This destroys all the iodine and chlorine to leave just the oxidized manganese or chromium).
5. Analyze per procedure and subtract the results of this test from the original analysis to obtain the correct chlorine results.

The sodium arsenite destroys only the chlorine and will not affect the manganese, as will the other dechlorinating chemicals.

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