DPD Powder

[bbqbrew]

How can you tell when your DPD Powder is too old to use for testing? :?:

 

[reebok]

I believe it starts turning dark/black.

 

[duraleigh]

Nope. If it turns your pool water (with chlorine) pink or deep pink, it is still good.

The only way you can tell that it's not working if it fails to turn the water pink and you know it has chlorine in it.

 

[reebok]

whoops, sorry. I was basing my answer on this post post121354.html and this post reagent-life-t7255.html
so if it's black it's ok?

 

[JasonLion]

The general wisdom has been to replace the DPD powder when it gets black. However, it has subsequently been discovered that it doesn't stop working completely, it just gets clumped up. If you break it apart enough to dissolve, it still gives correct results.

Of course, Taylor says to replace all reagents each year.

 

[Guest]

Black DPD powder has been oxidized so it's ability to form the red Wurster dye that we subsequently titrate with FAS titrant (a reducing agent that is also ruined by oxidation and changes pinkish to orange when bad).
IF the DPD powder is not completely black then it is still usable.
FWIW, I have seen DPD powder that was completely black but not clumped at all and clumped powder that was light gray. Clumping is a function of humidity, turning black is oxidation (exposure to atmospheric oxygen).

 

[bbqbrew]

My powder is gray and turns pink quickly when added to the water sample...so I guess I'm OK. Thanks!