FAS/DPD titration reagents


LifeTime Supporter
May 23, 2007
Montreal Canada
Just a thought: Why can't we use R-0001 and R-0002 instead of the DPD powder R-0870 in the water sample? It seems to me that the powder contains the both the phosphate pH buffers of R-0001 and the DPD of R-0002 (and some EDTA)? Is it strictly a concentration issue?

I did perform both tests yesterday, first with the powder and then replacing the powder with the combination R-0001/R-0002 and the results were within a few drops of each other. I was expecting the FAS to reduce the Wurster dye at the same rate with both DPD formulations.


TFP Expert
Platinum Supporter
LifeTime Supporter
May 7, 2007
Silver Spring, MD
I don't know the chemistry enought to be sure but I believe that the problem is that the R-0001 R-0002 combination will stop working at FC levels around 25 and higher, while R-0870 will work up to 50. For me the powder is easier to handle than counting ten drops from two different vials.

chem geek

TFP Expert
LifeTime Supporter
Mar 28, 2007
San Rafael, CA USA
It's even worse than that. According to Taylor's interference instructions here, the DPD reagents can bleach out with chlorine levels above 10 ppm, not 25. The FAS-DPD interference instructions here indicate that above 25 ppm the bleaching out will create a brown color (so at least you still know there is chlorine present) and that using more powder let's you test even higher chlorine levels -- somewhere else it said up to 50 ppm if you use more powder.