For High Range chlorine methods 10069 and 10070, should the 25 ml DPD powder pillow or two 10 ml DPD powder pillows be used?

Document ID

Document ID TE7823

Published Date

Published Date 04/16/2019
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Question
For High Range chlorine methods 10069 and 10070, should the 25 ml DPD powder pillow or two 10 ml DPD powder pillows be used?
Summary
The use of two 10 ml DPD powder pillows compared to one 25 ml DPD powder pillow.
Answer
For best results, customers should follow method instructions when deciding which reagent and how much reagent to use.

That being said, it is generally accepted that the use of either one 25 ml DPD powder pillow or two 10 ml DPD powder pillows can be used for high range chlorine methods 10069 and 10070. Depending on if the methods are being used with a pocket colorimeter or spectrophotometer, either procedure may be referenced in the method documents.  

With chlorine methods involving DPD, an excess of reagent is expected (excess DPD is colorless and won't contribute to the result). The 25 ml powder pillows have slightly more reagent in them than two 10 ml powder pillows. As a result, one 25 ml powder pillow may work better if the chlorine concentration is in the range of 8-10 ppm.

A side by side comparison can be done to verify if results are acceptable. In general, a side by side comparison is recommended anytime a method is modified.

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