Sorry John,

I have to disagree on your assertion that a DAB solution should be clear or
nearly clear.  Though the freshest of DAB solutions are fairly clear,
moderately brown solutions do not mean they are unuseable.  I have received
DAB which, though just shipped, turned quite brown.  This worried me a bit
but I tried it anyway since it was all I had on hand.  It worked fine with
no background. 

Glen Dawson	 Lead IHC Technologist
Dynacare Laboratories
Milwaukee, WI



-----Original Message-----
From: J. A. Kiernan [mailto:jkiernan@julian.uwo.ca]
Sent: Wednesday, December 13, 2000 1:20 PM
To: HistoNet@pathology.swmed.edu
Subject: Re: is there a simple way of testing DAB solution


On Tue, 12 Dec 2000, Tibor Ric wrote:

> DAB solution. I mean is it possible to check if the DAB solution still is
> working without setting up an application?
>
> Is there some chemical way of testing?

Add a drop of dilute hydrogen peroxide and a source of
peroxidase such as a drop of any HRP-labelled reagent.
The solution should go brown in a few seconds, ending
up very dark.

A DAB solution is unlikely to fail without any change in
its appearance. With time DAB is oxidized by air to give
brown products that can stain sections in their own right.
Therefore don't use a DAB solution that is light brown,
even if has only just been made up. A DAB solution should
be colourless or almost so.  Some batches of solid DAB
powder (or tablets) are brown and too oxidized to use. A brown
solution of DAB is likely to give brown background staining
that has nothing to do with peroxidase activity or
immunohistochemistry. I haven't seen this for several
years; perhaps the DAB on the market is fresher than
in the past. The solid, if it's OK to begin with, seems
to keep well for a few years at -20C. A solution of DAB
should be used as soon as it has been made up; don't
give it a chance to oxidize and go brown.

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