IR Sample Preparation

Casting a Film

You have probably made a sample for analysis by IR in your organic chemistry lab in the past. You likely placed a liquid chemical or solution between two IR inactive plates, or pressed a solid chemical into a KBr pellet, or something similar. Well, forget that (Well, don't forget it, you just won't use it here). Due to the amazing properties of polymers, it is often unnecesary for your sample to remain on a substrate when placed in the spectrometer. "How is that possible," you ask? Well I'll tell you. All you need to do is cast a free standing flim, something you can do with many polymers.

There are many ways to cast a film of a polymer. However, we will only discuss three ways which, as you might have guessed, are probably the cheapest and easiest ways.

You can cast a polymer film on:

• water
• glass
• a salt plate

Casting films is not difficult, but you have to do it right to obtain a good spectrum.

Now that you have formed your free standing film, ask your TA for a card (unless you used a salt plate) to mount your film on. This may be a special card made for the IR, or a business card. Yes, a business card. Business cards just happen to fit right into the spectrometer. Just cut a hole in the middle so the IR light can go through, and tape your film over the hole. Make sure no tape is over the hole (Why?).