IMVS Division of Pathology
The Queen Elizabeth Hospital
Woodville Road, Woodville, South Australia 5011
PROBLEM NUMBER 2
Using Calcium Carbonate to neutralise formalin
There are many ways to neutralise formalin - NOTE the term neutralise and not buffer. So that when something like tissue is added to the solution the pH begins to change. One is to add calcium carbonate but there are pitfalls with the use of calcium salts and the carbonate in particular.
For example formalin, neutralised with calcium carbonate usually becomes acid within 3 hours of exposure of tissue to the fixative solution when large pieces of tissue are fixed. This can cause the formation of formalin deposit in specimens which are rich in blood, such as spleen.
Therefore this fixative should only be used for small biopsies requiring less than 3 hours fixation, for which it is an excellent fixative giving better nuclear detail than conventional formalin buffered with sodium salts. One excellent reason for using it.
But remember that fixatives which contain calcium salts can also contaminate tissues with calcium artefacts. One excellent reason for not using such fixatives.
This is a section of fatty liver, fixed in formalin buffered with calcium carbonate and stained with von Kossa. Brownish formalin pigment is deposited in the sinusoids if you use your imagination, whilst black deposits of calcium can also be seen and which is attributed to deposits of insoluble calcium salts.
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© Roy C. Ellis 2002