Re: glutaraldehyde

Judy Seigel wrote:
>
> On Wed, 17 Mar 2004, T. E. Andersen wrote:
>
>
>> As a professional microscopist, I use glutaraldehyde on a regular
>> basis. It's odor is different, but every bit as pungent as
>> formalin, and all the same precautions should be taken.
>
>
> Thank you for the very interesting brief on gultaraldehyde... Now
> I'm wondering if you can answer the following -- do you know any
> reason why the glutaraldehyde would be better for the purpose than
> formaldehyde?

No, I see no reason for the glutaraldehyde to be better. It causes a
much higher degree of crosslinking of the proteins in the gelatin. This
is often of value in microscopy, but I don't see how this could be
beneficial for hardening alt-photo paper. On the other hand, it may well
prove to reduce the archival properties of the coating. I do not know
this to be the case, but I would not be surpriced if it did. After all,
the more cross-linked the proteins are, the more brittle the gelatin
will be, and the less of the protein molecules will be free to adhere to
the paper and image layers. Again, I do not know this to be a problem,
but it's fair assumption.

> The reason we changed from formaldehyde to glyoxal was that
> formaldehyde became generally unavailable. My understanding is that
> the reason was NOT the toxicity, that was the *pretext* -- the
> reason, I heard from those who supposedly know, is that it's used in
> making -- maybe it was crack cocaine, or like that.

This is all news to me. In Norway, there is no problem in obtaining
formalin (since it is classified as a dangerous substance, you need a
permit from the police, but if you have a good reason for wanting it,
and don't have a criminal record, it's no problem at all). You can not
readily store, and hence not buy a pure formaldehyde solution. The
commercial formalin contains a large percentage (ususllay 12-15%) of
methanol to stabelize it.
If you cannot buy formalin, you can always get paraformaldehyde instead
(it's a white powder), but then you will have to depolymerize it to make
the formaldehyde solution. Since this is pure formaldehyde, the solution
will only keep for about a week before going acid (formaldehyde will
disproportionate into formic acid and methanol, as well as some being
oxidized into formic acid), so it's not very practical (I do it only for
electron microscopy preparation, which needs really pure formaldehyde).

>
> I myself am satisfied with glyoxal, finding it much less painful to
> work with than formaldehyde, and as I've mentioned, no problem with
> yellowing once I started rinsing after the hardening. (Tho I don't
> put it in the gelatin, only a bath afterwards).

I have not used glyoxal (HOCCOH) yet (but I've bought a bottle to test).
It's similar to glutar aldehyde (HOC(CH2)3COH) in being a dialdehyde, so
it too, is cross-linking. However, the shorter the chain, the more it is
likely to penetrate into the tissue, so it is likely to be more
dangerous than glutaraldehyde, and I would certainly take all the same
precautions as with formalin. Again, I do not know this, but it is a
fair assumption, and I always try to give myself the benefit of the
doubt when it comes to safety of chemicals.

> However, for those unhappy with glyoxal... formaldehyde is available
> (or was a couple of years ago) by prescription at a decent sized
> pharmacy. Do you have any advice about which would be worse (or
> better?). My inclination would be the formaldehyde, since it's well
> tested for the purpose... at least 50 years, actually closer to 100
> if I remember correctly.

The formalin is currently believed to be the most dangerous of the
three. As I have said before, I'm sceptical, and choose to give myself
the benfit of the doubt. So, I treat glutartaldehyde and glyoxal as
equally riscy. If proper safety measures are taken, I see no reason not
to use the formalin (or pure formaldehyde). As you say, it has been used
and tested for a long time (*). However, if proper protection is not
available, it is better to use something else, or better, not to work
with chemicals at all. It's no good having made great pictures if you
end up with cancer...

Best wishes,

Tom Einar

> Thanks in advance for any thoughts on the subject...
>
> Judy

(*) Just a note on mixing the formalin with the gelatin solution prior
to coating. This may prove to be fine, I don't know. What I can say,
however, is that this practice results in coating the paper with
hardened gelatin, instead of hardeing gelatin already bound to the
paper. Also, doing this, the gelatin is fixed ("hardened") while still
in solution, whereas treating the coated paper fixes the gel-form of the
gelatin. This is likely to have a rather large impact on how the gelatin
adheres to the fibers in the paper, and may well alter the long term
ability for the coating to stay on the paper, as well as the bonding
between the gelatin and the image layer(s). Only time will tell if this
is of any practical consequence.
Received on Wed Mar 17 08:38:24 2004