Dear Dilip

I am not sure what is the question but I will try to answer anyway. The features (as well as intensity an ratio) you see are connected to four main things:

1. The material you measure.

2. The sensor sensativity.

3. The source emission 

4. Optical medium (e.g, KBr windows, type of ATR crystal etc.)

When dealing wite material type, there allot of substainses that make a significant spectral signiture around 2500-3400cm-1 for instance organic matter with several methyl groups. I don't know which material you measure so I can't relate to it.

The other 3 issues infulance significantly on the signal. There are numerus types of sensors which are more sensitive to one spectral range and not the other. The source can differ between different FTIRs and may influence on the final sensitivity. And finally, the optical mediums can absorb in different ranges adding more interference.

My advice to you ( if you sure your material has substaintial spectral signiture at the region of interest) is to check the background single beam to see if without the measured sample enough radiation intensity reachs the sensor at the region of interest. Maybe you need to switch  a source or a sensor. If not than you should think again on the measured material.

Dilip, either you don't have any prominent signature of the material in that range or check the amount of sample you are taking. 

Hi

Find in attach, a very excellent book in spectroscopy. You may find the answer of your question their.

Mr./Miss/Mrs Sharma,

As I have understood, most probably, you have problems with conventional IR-spectra of peptides and/or proteins. Is it? because of with oligopeptides the profile is relatively determinable. If yes, then, in general, interpretation of IR-pattern of such as objects by conventional IR-spectroscopy is a highly speculative task. So, minimum you should involve a polarized IR-spectroscopy in order to determine the modes and to assign them [Ref. 1]. But even this method has limits regarding complexity of the IR-profile.

In other words, an IR-spectrum expresses the energetics of a system and it is the same both measuring vibrations in transmissions/absorption or reflectance modes (conventional IR or ATR).

[Ref. 1] Kolev, T.; Spiteller, M.; Koleva, B. (2010) Spectroscopic and structural elucidation of amino acid derivatives and small peptides: experimental and theoretical tools, Amino Acids, 38, 45-50.

Thank you very much for your suggestion. its really much more clarify me.

now moving ahead I am working with pharmaceutical impurities in API.

And with regard Mr. Oz kira, I need some more phrases about spectral signature?

and thank you all of you for such nice information.

 Did not understood your question. I will gladly try to answer but please clarify what you meant...write me a private massage and elaborate as much as you can. you can also send me a sample of your spectra for me to examine. 

Oz

The weakness of the IR bands you observed may be due to the uncrystallinity of your sample. You could repeat doind IR spectra after doing more crystallization.