[Histonet] paraformaldehyde crystals v Prills

John A. Kiernan jkiernan <@t> uwo.ca
Tue Jan 17 11:55:20 CST 2006

Carl Hobbs wrote:
> Many of our Groups use paraformaldehyde crystals ( Sigma P6148) to make up
> their solution of formalin. Works very well; 4g + 1tab PBS + 6microlitre
> 10MNaOH.....stir overnight. Dissolved completely:pH7.2
> I am trying to get away from using this paraformaldehyde: it is very light
> and prone to spread around the fume hood when it's weighed out.
>     So, I bought PRILLS from Sigma:Problem is, they just do not dissolve
> completely, unless I preboil the water.( heating to 60C is not hot enough to
> dissolve the Prills.
>  I have tried all combinations of the formulation above( eg: no NaOH,
> dissolving PBS tablet before adding paraformaldehyde).
> I want the procedure with the least risk; boiling may be a higher risk than
> the spread of powder.
> NB: I cannot turn down/off the fume hoods, for the weighing of the
> crystals( which behave more like a very fine powder), hence my desire to use
> the heavier Prills.
> Be grateful for any insights.
> Carl

You can avoid the fine powder and insolubility
problems by making your fixative from formalin
rather than paraformaldehyde. 

A good mixture, shown to be OK even for electron
microscopy, is that of Carson FL, Martin JH & Lynn
JA 1973, Am. J. Clin. Path. 59:365-373. Its
composition is:
Formalin 100 ml
Water 900 ml
Monobasic sodium phosphate, monohydrate 18.6 g
Sodium hydroxide 4.2 g
The pH is 7.2-7.4 and the solution can be kept for
several months.

As always, don't rely on the accuracy of this or
any other email! Consult the original paper before
making and using the fixative.
John A. Kiernan
Department of Anatomy and Cell Biology
The University of Western Ontario
London,   Canada   N6A 5C1

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