Hi

It depends on which IR range you need to measure and of your measurement device construction type. I'm using Easy Diff by PIKE and I have to types of measuring cups smaller and bigger one. When I have only small amount of sample I use smaller cups. The most important to obtain good quality spectrum is to focus beam on the sample (and in my DRIFTS I can adjust sample position by special screw - so even if the cup is not full of sample in most cases I can adjust it by sample positioning (up, down) and focusing (trying to have the best signal level for background) - the amount of sample must be bigger for FIR range (because in this range the beam penetrates more the sample).

If I intend to measure in middle IR range (400-4000cm-1) the sample should be diluted (mixed with KBr powder with a little bigger sample concentration then for KBr pallets preparation) if we don't dilute the sample spectra shows artifacts mostly intensity and shape artifacts - (best to check it on the sample of known spectrum).

Usually, you don't need to dilute for NIR range.

So to conclude : in most cases (in MID IR measurements) small amount of sample it's not a very big problem because most often sample should be diluted, and/or it may be adjusted by proper sample focusing.

Regards

Maja