Re: Formaldehyde recycler & assaying
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From: | "J. A. Kiernan" <jkiernan@julian.uwo.ca> |
To: | RSRICHMOND@aol.com |
Reply-To: | |
Date: | Fri, 03 Sep 1999 10:07:57 -0400 (EDT) |
Content-Type: | TEXT/PLAIN; charset=US-ASCII |
On Thu, 2 Sep 1999 RSRICHMOND@aol.com 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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