[Nadja]

Hello,
I have a problem cleaning my diamond crystal for an IR-ATR accessory. The crystal looks visible clean, but when one runs an IR spectrum of it, it shows some traces of protein. I have tried washing it with water, ethanol, 0.8M sodium hydroxide, some special laboratory cleaning solution, and even with some HCl. But nothing seems to remove the protein. Unfortunately I don’t know what the protein is.
Does anyone have any ideas on how it might be cleaned?

[gluedudeguru]

If it is actually dirty, acetone usually does the trick, it is what i have always used.  Perhaps that this blib your seeing would be none existent with a proper background, especially if it looks clean.  We are sure your not refering to CO2 and water right?  What makes you think its protein? Does an IR/ATR even do protein?

ACETONE

[Nadja]

Yes we are sure its not water or CO2.
We see Amide I and Amide II bands. And when attempting to clean with NaOH and HCl we see protonation and deprotonation of carboxyl groups.
It feels like something formed a thin layer (film) on the crystal and is reacting with the solvents I'm trying to remove it with.

[KeithM]

Yes, I agree with the film theory, something has stuck on the surface. Try "polishing" it off. Use some cerium oxide, Cerox 1650 would be good, on a soft cloth.

What country are you in? I could send you a bit if you are in the UK

[Nadja]

Thank you, KeithM.

Unfortunately I'm in Stockholm Sweden. I'm sure that our department should have it somewhere, I'll ask around.

[doc30]

We've had similar issues. Strong caustic won't hurt the diamond, but it might attack the adhesive holding it in place so be careful. How strong are the absorbance bands in the residue spectrum? You could clean with caustic, run a spectrum, clean again and run a second spectrum to see if the cleaning is removing any material. Can you look at the crystal under a low power microscope or magnifier and see if it is scratched or if there is a solid chunk you could scrape off with a microscope probe?

[AlloyNB]

You can polish a new clean Si crystal - it's not so difficult IMHO

[Fleaker]

If it's a diamond you're using, 70% perchloric acid takes protein off a treat.