In addition, there are a number of unique prep methods. For example, with polymers, it could be hot press films or solvent cast films. This is in addition to nojol blends (nujol is something you hear in IR and not much of anywhere else), KBr pellets, and straight liquid films. The liquid films are usually put between two NaCl disk or two KBr disks and run. If you don't control the thickness with a spacer or some other method, well, the absorb bands will be way off. For this reason, often, peaks are referenced in IR work. Not straight absorb ance calculation, but the calculation is done relative to a standard peak in the spsctrum. A start for you to look up. Good luck!