DPD powder experiment

[Poconos]

Been reading here for a long time about deterioration of DPD powder. When it gets clumpy and dark gray or black, it's no good or maybe questionable. When in doubt, run an experiment. Taylor R-0870, same as in the PS-233 kit. Took a small amount from same batch and let it sit in a container, sometimes open, sometimes closed, in a high temperature and humidity environment (Northeast PA with no A/C) for probably 6 weeks. Looked awful. Did a 25 ml sample of water just now with good powder and yucky powder after declumping it. Both tests identical, 17 drops, 3.4 ppm. You can draw your own conclusion.
Al

[CrisL]

I did a similar thing last year. I got new dpd powder at the beginning of the year, but still had some old studd left from the year before. I tested tho old grey stuff against the new and came up with the same results - but by mid year (about now) I did the same test again and came up with about a 1/3 decrease in the reading with the old powder. It was really dark grey and clumpy by then. Unfortuantely, there seemed no way to tell by eyeballing it when the stuff really started to deteriorate in quality.

[DavidD]

Thanks Al! I kind of suspected but wasn't sure so I kept dumping the "lumpy". Not any more.

Dave

[Poconos]

Interesting about the 1/3 decrease in reading. I still have the powder samples and will try a couple more comparisons, probably at end of this season and next year. Chemistry isn't my bag so I have no idea. Chem_Geek...any thoughts on this?
Al

[PatL34]

I have started to keep the DPD powder vial in a silica gel bottle, and am waiting to see how it turns out.

Pat

[waterbear]

My understanding is that as long as the color has not turned to a dark grey it is still usable. Light grey and clumpy is ok.