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

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Don Hammer

>>I would suggest they toss it out and make their own 10% Formalin. (take 
control)  It's the simplest "recipe" in the books. <<

Actually it's not, to judge my the Samurai Pathologist's experience. Small 
labs commonly prepared their own phosphate buffered formalin until well into 
the 1980's. In my experience most of them did it wrong, with significant 
adverse consequences in the slides. 

The major problem was the dibasic sodium phosphate (Na2HPO4). This material 
is available both in the anhydrous form, and as a heptahydrate salt which is 
nearly half water. Older books do not specify which form is to be used, 
though they mean to specify the anhydrous form. But since the heptahydrate 
salt, being nearly half water, is the cheapest, that's what the lab manager 
(the only person with access to the catalog) orders. Obviously in this 
circumstance you can recalculate the formula, but that requires a high school 
chemistry course, which the pathologist has forgotten and the histotech never 

Another common and disastrous error - I've seen it several times, and confess 
to having made it myself once - is to go to all the trouble of weighing out 
the buffer salts and getting them to dissolve - and then forget to add the 
formaldehyde at all!

Buying ready-made neutral buffered formalin is a significant expense and an 
environmental absurdity, but in my experience it's the best way to go.

Bob Richmond
Samurai Pathologist
Knoxville TN

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