[Histonet] (no subject)

Dr. Michael Gudo (Morphisto GmbH) michael.gudo at morphisto.de
Sat Jan 25 06:46:10 CST 2020

Dear Kate,

very interesting question.

The both substances you mention are a bit difficult in this respect. In a general crystal structure phosphortungstic acid has 44 water molecules and phosphormolybdic acid 28 molecules of crystal water. This would mean, that for a an exact 5% solution you would need around 72,62 g of phosphortungstic acids and 72,73 of phosphormolybdic acid on 1.000 ml water. The standard for a 5 % solution of a solid substance without crystal water would be 52,63 g per 1.000 ml.

However, in this case, the substances do not exactly have this number of water molecules in the crystal structure because they loose water and they are hygroscopic. This means that they take more water molecules from the air and that they partly melt in the bottle, if leave it open to long. 
 „• x H20“ - does not mean, that the manufacturers don’t want to give this information, its because it cannot be known exactly.

For these substances histological practice is to ignore the crystal water and to use the 52,63 g substance for 1.000 ml of water to get a 5% solution (or to add 5 g substance to 95 g water).

This does not have an crucial effect, because the mordanting process for which these acids are used has to be controlled by microscopy anyway. So if you want to make it faster you can add more substance. The important point is only, to make it always the same way.

Kind regards

> Am 24.01.2020 um 16:51 schrieb Kate Davoli via Histonet <histonet at lists.utsouthwestern.edu>:
> I'm all set to DYI my own phosphomolybdic/phosphotungstic acid solution for
> running a Masson Trichrome, but I see that the former reagent was
> purchased as "phosphomolybdic acid hydrate".
> All the recipes I have seen call for just "phosphomolybdic acid" but that
> is not a reagent that appears to exist without the water molecules coming
> along for the ride, unless you want to invest in chromatography grade
> stuff, which I think histology folks probably don't routinely do.
> The recipes all call for equal gram amounts of each of these crystals, so
> here's my question:
> Do I calculate how much weight the water is taking up and add more
> phosphomolybdic acid crystals (to account for its tagalong water molecules)
> than called for in the recipe?  Or are these recipes already assuming that
> phosphomolybdic acid HYDRATE is the reagent you have on hand, and I should
> stick with equal amounts?
> This question is somewhat complicated by the fact that the molecular
> formula on the bottle is listed as H3Mo12O40P.XH2O ... which I think means
> the manufacturer won't bet on exactly how many water molecules are involved.
> Any advice appreciated!
> Katherine Davoli, BA, HTL(ASCP)CM
> Supervisor & Lab Manager, Tissue Culture & Histology Core Module
> Ophthalmic and Visual Sciences Research Center
> Department of Ophthalmology, University of Pittsburgh
> Mail Stop Code: EEI010901
> 930 Eye & Ear Institute, 203 Lothrop Street
> Pittsburgh, PA 15213
> (412) 647-8256    davolika at upmc.edu and kdavoli at gmail.com
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> Histonet at lists.utsouthwestern.edu
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PD Dr. phil. nat. Michael Gudo
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