Dear Zahra Nobakht Nobakht ,

After seeing your image, the peaks do not correspond to KBr, since this should be transparent to the FTIR wavelengths. Fortunately, they just coincide with water signals, so you are basically seeing water. KBr tends to absord water very easily. To avoid this issue, normally in my lab we keep it in a dissecator, but 24 hours before using it, we put it in a oven, at 105C to eliminate all the moisture it might have absorbed.

Try to do this: put it in an oven, above 100C during 24hs, and use it (try to make a pellet of pure KBr), and you should not see any signals at all.

Hope it helps!

The stretching at 3500 cm-1 infer the presence of water or oxidaztion of KBr pellet. You can store KBr in air tight tinted glass containors or tinted dessicators if possible. Also, the stretching at 1640 cm-1 infers to the dry KBr with a sharp and intense stretching.

Hi, thanks for your reply I do exactly what you said, the KBr powder is always kept in a desiccator and dried in the oven 24 hours before the test. Is it possible that KBr has an irreversible reaction with water that does not remove water even after drying?

Dear Zahra Nobakht Nobakht ,

After reading your reply, it sound a bit strange about an irreversible reaction of water and KBr, but nevertheless, you could try drying your KBr, under vacuum as well, to ensure that you are able to remove any water remaining. Also, the observation given above about the possible oxidation might worth considering storing the KBr in a tinted container. If the KBr is already oxidized, then I believe it is not possible to obtain suitable KBr again, or at least, I do not know how to do it.

Maybe you can check in Google Scholar if it is possible to re-obtain pure KBr after it is oxidized.