OzleMM,
your question has been ask before (https://forums.noria.com/eve/forums/a/tpc/f/136604995/m/6401032962).
in FTIR analysis you have to compare the original FTIR graph (fresh oil) to the sample FTIR graph.
Just for sharing, what i do:
Max Oxidation = 0.5 Abs from its original value
To analyze oxidation, find the peak in 1750 cm-1
Max Nitration = 0.3 Abs from its origina value
To analyze nitration, find the peak in 1630 cm-1
For soot analysis, I prefer to use BLOTTER SPOT TEST.
regards,
Nurudin