[argus]

How can we determine soots and glycerol in oil samples using FTIR? What are their wavelengths?

[Arkcon]

Here's an acceptable start:  http://www.machinerylubrication.com/Read/1109/oil-degradation-spectroscopy

There may be other resources for you if you Google them.  This is a lubrication webpage, perhaps you meen cooking oil, but the general idea remains the same.