On Fri, 26 Nov 1999, Scott Schmitz wrote:

> We have been having trouble with our immunoperoxidase
> staining.  The chromogen has been getting lighter and
> lighter in staining until finally today I had no staining.

   My guess is that your stock of hydrogen peroxide
   has deteriorated. The 30% solution has a way of
   dying unpredictably. One cause is coming into
   contact with almost any substance, including
   phosphate ions and metals.

   You can get a solid compound called urea hydrogen
   peroxide that is more stable: You treat it as if
   it were 35% and just weigh a bit out to make a
   stock solution (1% or whatever) in water that you keep
   in a clean glass bottle and change every week - or
   every day if you want. UHP is greatly superior
   to 30% hydrogen peroxide, and it seems to keep for
   ever in the fridge. I've had the same jar for about
   5 years.

 John A. Kiernan,
 Department of Anatomy & Cell Biology,
 The University of Western Ontario,
 LONDON,  Canada  N6A 5C1