Chemistry question

Dingle_berry

I've forgotten all my chemistry and can't find an answer through google.… any chemistry fans out there have any ideas?

In work we preserve biological samples by removing the water and replacing it with paraffin wax. This is done on a machine, under vacuum at about 60°C, no light gets into the chamber. The process is Formalin, 70% alcohol (Industrial Methylated Spirits), 100% IMS, Xylene then molten paraffin wax.
Recently the machines got clogged with a white precipitate - cloudy/milky in solution but chalky when dry. The engineer said it was because the 100% IMS and the Xylene mixed - this formed the precipitate. But the reason we use these two solutions is because they are miscible, that they don't react in this way? I'm wondering if it was the formaldehyde in the formalin mixing with xylene?

SOL

The white chalky solid must be wax... I guess what happened is that the wax precipitated out when it was dissolved in one solvent and the other was mixed in.
At a guess I'd say that the wax is more soluble in xylene so when you add in the IMS it will precipitate out as a white crumbly solid...


I'd say it's unlikely that what you are getting is a chemical reaction... just a solution - precipitation thing going on.

Also, and this is entirely out of interest, what exactly do you preserve this way?

Dingle_berry

Yeah the only reason we use xylene is as a "bridge" between the IMS and paraffin wax. It makes more sense that there was wax in the xylene and the IMS caused it to precipitate - just there shouldn't have been wax in the xylene that was affected, the wax is pumped in after the xylene is drained. A seperate bottle of xylene is used to clean the chamber after the wax…
If I get a free minute in work I might "experiment" Do you think the temperature is important, as I don't want to go heating xylene to 60°!

SOL wrote: »

Also, and this is entirely out of interest, what exactly do you preserve this way?

It's human tissue. Look up "histology" in Wikipedia, that's what I do! Lots of chemistry in it, I should really be better at chemistry!

krd

Dingle_berry wrote: »

It's human tissue. Look up "histology" in Wikipedia, that's what I do! Lots of chemistry in it, I should really be better at chemistry!

The trained scientists who perform the preparation of histological sections are histotechnicians

Well you better get trained up on some chemistry, Mr. Scientist, better'ent you.


I know sweet FA chemistry, but I know my father (who did know his chemistry) did stuff with paraffin. There was some trick to getting paraffin to stabilise in a mixture that he made - he had a waterproofing mix. Paraffin has some way of separating from other solvents - but he had some trick to make it stick. I don't know what his magic trick was.

Dingle_berry

krd wrote: »

histotechnicians

Well you better get trained up on some chemistry, Mr. Scientist, better'ent you.

We prefer the term Medical Scientist. Don't ask me why!