Re: Formaldehyde recycler & assaying

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From:"J. A. Kiernan" <>
Date:Fri, 03 Sep 1999 10:07:57 -0400 (EDT)
Content-Type:TEXT/PLAIN; charset=US-ASCII

On Thu, 2 Sep 1999 wrote:

> I have no experience with the formaldehyde still, and that's what I'd like to 
> know more about. In my experience, assaying the formaldehyde and mixing the 
> buffer salts would be beyond the skills of most laboratories (I NEVER saw a 
> lab prepare neutral buffered formalin correctly). The only way I can imagine 
> this being practical is with kits of pre-mixed buffer phosphates, and I've 
> been surprised that nobody ever made these available. Are they available now?

   If you're really keen on having a physiologically buffered and isotonic
   phosphate solution, then Dulbecco's balanced salt solution is the one
   to go for: kind to cultured cells and doesn't need a CO2-enriched
   atmosphere to maintain its pH. It is, in fact, PBS with cell-friendly
   amounts of potassium, calcium and magnesium ions. It's fairly easily
   made by weighing and dissolving 6 cheap ingredients, but even more 
   easily generated by chucking a little pot of pre-mixed Dulbecco powder
   into a litre of distilled water. Several companies sell the little
   pots of powder. It costs more but saves time, and there is nothing
   secret about what you're buying in the kit, so it's OK to use it in
   research. The recipe was published in 1954: J. Exp. Med. 99, 167-182.
   (This popular solution is a by-product of an otherwise largely
   forgotten publication.) 

   Assaying the recovered formaldehyde should not be necessary for most
   purposes because the concentration of this compound in a fixative
   solution is not at all critical. The concentration of monomeric
   methylene glycol and low polymers (active in fixation) increases
   with the dilution. Consequently it's possible to use neat formalin
   (37-40% HCHO) or a 1:100 dilution (0.4% HCHO) without changing the
   chemical reactivity with proteins. It's always necessary to allow
   enough time for formaldehyde fixation (a few days, at least) and
   the much shorter times currently used in routine histopathology
   produce tissues fixed only partly by formaldehyde and mostly by the
   coagulative action of the solvents used for dehydration. 
   For everything you could ever want to know about formaldehyde,
   see the book, "Formaldehyde" by JF Walker. 3rd edn, 1964, Reinhold, 
   New York.

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

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