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Dear colleagues,
this is not the first time someone has had supplied to them or has
formulated supposedly 10% NBF which has turned out to be something much
less, and with loss of irreplacable biopsy material and all that entails
(God help the patients). This happened with a commercial supply here in
People should insist upon a "Formaldehyde Assay" by an Independent Authority
on the material received (Not just the supplier's own test lab- that's a
conflict of interest!).
You can also check this out yourself, which is not difficult:-
Measure 3ml of solution with a volumetric pipette (don't use your mouth)
into a 100ml conical flask. Add 50ml of 1 Normal NaOH (also with
vol.pipette). Add 50ml of 10vol Hydrogen peroxide. Insert small flea and
place in steamer (your HEIR steamer is fine for this) for 2hrs , swirling
contents every 15-20 mins (wear a glove). Repeat this in duplicate (to help
with titration because you will almost certainly overshoot the end point,
and include a blank without any sample.)
When cool, titrate with 1 Normal HCl using Phenolphthalein indicator with a
50ml burette. (A mixer with burette stand and clamp fitted is ideal) against
a white background. (Other indicators can be used eg. BCP or BTB but these
may not be as crisp)
Each ml difference between blank and sample represents 1% w/v of
Remember that 4% Formaldehyde = 10% Formalin.
If you think this takes too much time then only test your conc. formaldehyde
as a check on your supplier and insist on the same batch no. for say 3 or 6
months, and of course if you know the actual true % of Formaldehyde in your
raw material, you can correct for low values and adjust your dilution
accordingly so that you always get a final concentration of 4%- I've been
testing my raw material for over five years now as a double check and can
assure you it is worthwhile "'cause we didn't get caught out" producing non
4% NBF unlike some others who did and were!

Yours in Histology,
Mike Rentsch. Scrutineer Histomail.

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