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Question Regarding Free Bromine Testing Using DPD-1

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We recently received an inquiry from 'TJA' who asked, "I'm testing for free bromine with HACH DPD-1 25 ml powder pack using a LaMotte 1200 Bromine colorimeter. How long should I wait from adding the reagent packet to testing the sample with the colorimeter for accurate free bromine results? It seems that the longer I wait after adding the reagent, the higher the ppm results become (does not make sense to me). Thank you for your time."

We're not all that familiar with the LaMotte 1200 Colorimeter so we looked it up real quick. It LOOKS like the machine uses a 10mL sample size and if so, then the 25mL reagent packet is a bit too much reagent for the sample size.

Another possible influence: Temperature.

In cooler samples reagents take longer to function so the color development takes longer

Another possible influence: Temperature. In cooler samples reagents take longer to function

As for the time it should take for a sample at 'ambient' or what they call 'room' temperature, to react fully with a reagent, you will need to consult the meter's instruction manual OR the check the test reagent's instructions. As a general rule, though, we THINK a typical DPD-1 test for free bromine should get read (interpreted) within 15 to 30 seconds after the addition and dissolving of the reagent in a sample.

As an example...   DPD-1 ReagentStrips for 10mL Water Samples

DPD-1 ReagentStrips - "Simply dip the strip into a 10ml water sample for 20 seconds with back and forth motion, remove, & discard the strip, and immediately read the test sample in your chlorine meter. ReagentStrip DPD-1 performs flawlessly with a wide range of existing meters from manufacturers such as Hach®, LaMotte®, Orion®, WTW®, etc."

DPD-1 Test Reagent