FTIR is mainly used for the qualitative detection of functional groups. It is not the best judge for quantitative estimation of componants. However if you want to get an estimate, you can compare the area of one distinguished peak of the componant of interest to another peak that is fixed in all casses. 

hope this helps

Kartikeya,

Beer's Law answers your question.  The absorbance (A) is equal to the extinction coefficient (ε) for the peak times the path length (l) times concentration (c) or A= εlc .  For a particular peak absorbance will vary directly with concentration if path length through the sample is constant.

If your are using transmission-FTIR (or in a lot of cases also the ATR-FTIR sampling method), and your samples are uniform solutions/mixtures, they will obey Lambert-Beer’s law, just like when you use e.g. UV-VIS transmission spectroscopy. Just be sure to use absorption instead of transmission though! If you use ATR-FTIR you should read a bit into the basic theory and principles of the ATR method. With a bit of care and precautions you can use ATR-FTIR just as a special case of transmission FTIR, e.g. Lambert-Beer’s law is applicable. In a few cases that should take care:

If you have particles in your sample (i.e. a slurry) and you are using ATR sampling you should take more care: Only particles with sizes smaller or comparable with the evanescent wave (roughly 1 micrometer) will contribute significantly to the spectrum. Therefore, if you have a slurry sample with lets say above 10-20 micrometer crystal and you are using a diamond ATR-FTIR spectrometer, you will in practice only see the liquid phase of the slurry, and the particles will seem “invisible”. However in a suspension of nanoparticles, they will contribute to the spectra along with the liquid phase.

Generally, you should take more care for solid samples where variations in the components refractive index. You should look up “ATR-correction” - most spectrometer software has a build in algorithm for this, but you should know a bit about how the correction works. Especially if you are comparing mixtures of a low refractive index compound with a high refractive index compound, you should be very careful as the quantification becomes more non-trivial.

But for uniform liquid samples ATR-FTIR is a very powerful quantitative technique. You could use peak height of isolated peaks. But a much better option would be to use the band areas in deconvoluted spectra (you can get stared with deconvolution spectra with a lot of different software, I can recommend the program PeakFit)

good luck

Best regards,

Andreas

Dear Dr. Kartikeya Dixit:

the distribution of your "particular component C" between the samples S1 and S2

does not matter. Important is the TOTAL concentration of component C in your

2-componet system - just like Dr. John Hiltz - commented above.