Re: 10% NBF. How to check the concentration.

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From:Tony Henwood <>, "Mohammed, Sayeed" <>
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Dear Mohammed,

> Hi Histonetters.
> Recently a neighboring lab had a problem with two different batches of
> formalin from the supplier. One batch was not fixing the tissue( routine
> tissue ) properly, whereas the other batch fixed it in the same time and
> same type of tissue. The supplier did not have any answers except " we
> checked the batch and found nothing wrong with it." The techs in the lab
> checked both batches for pH and found no difference. So, my suggestion was
> to check the concentration. Any netters out there have an idea. 
There is a simple test to determine whether formalin is above or 
below 4% as follows (it is also on my web page):
A useful quality control procedure for formalin concentration has 
been described  by Jaspers (J. Histotechnol., 10(4):263-266, 1978). 
It can be used to titrate a solution of buffered formalin whose 
concentration is not known: 

Take 10ml sample of buffered formalin. 
Add 50ml of 2.4% Sodium Bisulphite and allow to react for 15min at room temperature. 
Add 1ml Schiff's reagent 
If the solution turns deep violet, the formalin is usable for fixation (ie in excess of 4%). 

hope this helps, Tony

Tony Henwood
Senior Scientist
Anatomical Pathology
Royal Prince Alfred Hospital

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