Longish - Re: Picric acid in Van Giesons

From:"J. A. Kiernan"

"Johnston, Kathy" wrote:
> Does anyone out in Histoland have a substitution for Picric Acid in their
> Van Gieson counterstain.  I'm trying to eliminate the need for PA here as I
> always have a heck of a time ordering it in, not to mention there has got to
> be something better to use (i.e.. safer).

First the safety stuff.
Picric acid in Van Gieson's stain, Bouin's fixative etc is
"safe" as long as you don't drink it or bathe in it. 
The famous explosive properties are of the dry solid,
not of solutions. In labs the solid is always stored wet, 
so no part of the mass ever reaches even 100C. (Dry picric
acid melts at 122C and explodes if the temperature in 
part of the mass reaches 300C; this can occur from 
percussion but ordinarily it needs a detonator or a fire.)
There have been plenty of Histonet discussions of this
in the past (see http://www.histosearch.com), some with
recommended further readings.

I don't know of any simple substitution. The requirement
would be for a yellow dye with small hydrophilic anions.
The nearest ones that come to mind would be monoazo dyes,
(see Richard Horobin's Chapter 10 in Conn's Biological 
Stains, 10th edn, 2002) but these all have appreciably 
larger molecules than picric acid. They have all been 
around for more than 100 years; people must have tried 
them and failed.

It's worth noting that the stains derived in principle
from Van Gieson (such as picro-indigocarmine, picro-aniline
blue and picro-sirius red) all use picric acid for the
cytoplasmic stain and to prevent the other dye from binding
to tissue components other than collagen fibres. 

R. D. Lillie published a 47-page paper about stains of this
type in 1945, reporting on all sorts of dye combinations.
He went on investigating and improving these methods until
the mid-1960s. Holde Puchtler and her collaborators also
published very thorough studies, different from Lillie's, 
in the 1960s. There is still uncertainty and controversy
about just how the combination of dyes produces its effects.
For a recent review that puts a new slant on all this (and
on staining mechanisms generally), see  Prento, P (2001) 
Biotech. Histochem. 76:137-161.  

John Kiernan
London, Canada.

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