dissolution of coccolithophores

[Rene]

I've got a question I hope a chemist can answer.

Samples for coccolithophore analysis were normally preserved in buffered formalin according to Throndsen (working conc 0.4% formaldehyde, 0.2% hexamine= hexamethylenetetramine). Now that formalin has been outlawed, we are looking into neutral Lugol as an alternative (working conc 0.2g/l iodide I₂, 0.4g/l potassiumiodide KI en 0.4g/l sodiumacetate NaAc).

That seems to work fine, here is an example of an Emiliania cell, and a couple of loose calcareous scales after 13 months in storage in neutral lugol's.


(60/1.4, brightfield)

The detail on LM level is basically similar to that of formalin fixed material.

HOWEVER, if I mix both the formalin material + the lugol material, the coccolith scales dissolve!!! Only naked protoplasts survive:



No idea why, my gutfeeling is it has to do something with the iodine mix combined with the hexamine buffer. As far as I can judge, the mix is still alkaline.

Can someone offer an explanation??

Thanks, René

[Holger]

Hi, René,

well, I'm guessing, but iodine  may act as an oxidizing agent, resulting in the formation of formic acid from formaldehyde in situ. However, in the presence of excess of an organic amine, that should not matter so much...

Regards,
Holger

[Rene]

Yes, my idea as well.
In addition, iodine (brown) is shifted to iodide (colourless) in alkaline condition, and the mix is colourless. That's why I think the mix is still alkaline. Unfortunately I do not have access to a proper pH meter so cannot do a direct check.

Thanks, René