Currently I'm doing research involving photo-polymer which contains unknown substances. Is it possible to detect each component of the substance by using FTIR? Will it be able to separate the photoinitator component, the monomer, and the oligomer?


Not really... FTIR is more like a fingerprinting device. FT basically means identification is done with your computer. But you just have one line/graph that represents all three together. It doesn't separate the spectra; but with practice you can "see" things that are mixed, although some chemical tend to dominate the spectrum. Also, the FTIR device that you get will probably have a program that can help interpret peaks (which I have found to be utterly useless). The real way it (the spectrometer) works is by searching through the library. Again, the device you get will come with a library, but it's usually not worth anything. You will need to create your own library including all of the possible combinations (identify/name each sample that you make).

I would say that with enough practice and repeated sampling (building a library of known mixtures), that you could might be able to identify an unknown sample as a mixture of the components; and possibly the amounts of mixed components (depending on what they are, exactly).

In other words, let's suppose you have decane, benzene, and acetone. You will need to create a library like:

  1. pure decane
  2. pure benzene
  3. pure acetone
  4. 5% Benzene in decane
  5. 25% Benzene in decane
  6. 50% Benzene in decane
  7. 75% Benzene in decane
  8. 95% Benzene in decane
  9. 5% acetone in decane
  10. 25% acetone in decane
  11. 50% acetone in decane
  12. ...
  13. 35% acetone 55% decane 10% benzene
  14. ...

And you should run each sample 3 times. Then, after you have exhausted the list of known culprits, you should be able to nearly identify an unknown sample which is known to be mixture of these three chemicals (supposing that the amounts of each are what is unknown)... but be sure to run/analyze the unknown sample at least three times (adding it to the library each time) for best results.

Now with regards to photoinitiators... if using metals (like silver), it might be more tricky. IR Spec is most useful for organic chemistry.

  • $\begingroup$ ‘IR spec is most useful for organic chemistry’? I argue it’s not useful at all … $\endgroup$ – Jan Aug 26 '16 at 23:35

You will clearly be able to produce a difference spectrum, light on vs light-off, and possibly identify some groups therein, but as to identifying species, I would not hold my breath ! You should try something like MALDI, I'm sure it would be more fruitful and is already used in polymer chemistry.


FTIR wouldn't help you in find out the exact structure of a compound, but rather gave you information about the functional group present in a molecule. If you want to find out the exact structure of a compound you need Nuclear Magnetic Resonance( NMR) spectroscopy.


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