Hi!
I'm working with erythritol (sugar alcohol) which was under thermal treatment at different temperatures. I did an analysis with FTIR and since I'm a complete beginner at it, I'm not sure if the broadening of the peaks between 2800 and 2500 means something or not.
The only clear changes after heating the sample that I can see are 2 peaks: 1642 ( Alkenyl C=C stretch) and 1716 (ketone, carboxylic acids and aldehyde).
Thank you very much!
The line broadening in FTIR spectra could be due to changes introduced in the chemical environments when a specific element (H, C, etc.) may be bonding with other chemical groups (e.g., extensive hydrogen bonding is observed with other hydroxy groups, etc.). The chemical groups may be within the same molecule (intramolecular bonding) or they may exist between neighboring molecules (intermolecular bonding). In any case, the impact of bonding of an element (e.g. H, C, etc.) is to produce measurable band broadening, which may be accompanied by changes in the mean absorption frequency (often lowering the mean frequency). You may look at the following publication on “Interpretation of Infrared Spectra, A Practical Approach” as an example using the following link: http://www3.uma.pt/jrodrigues/disciplinas/QINO-II/Teorica/IR.pdf
One may also compare FTIR spectra with Raman Spectra and look for changes in the Raman peaks associated with the related bonds. The IR forbidden lines often appear in Raman spectra due to local bond perturbations and broken bond symmetry. IR spectra are representing atomic motions producing dipole radiation that is normally not Raman active mode, while Raman active modes are produce by changes in the polarizability, which normally are IR forbidden mode. However, changes in local bonds allows for appearance of ordinary forbidden modes in the Raman spectra that can be linked back to changes in the bond associated with the related IR mode.
Mr. Alferez,
First of all there is a lack of broadering. Second, there is some perturbation of the intensity, but it cannot be evaluated on the base on the shown spectra. Can you provide IR spectra in T mode however with baseline correction? In addition there are needed the integral transmissions or absorbances.
I agree with Dr. Ivanova. These are the spectra that you have just registered. Spectra preprocessing (i.e. baseline correction) should be performed first.
I have recently been dealing with temperature effects on another sample, and
I suggest that the first look at the spectrum cannot give a full answer. I can propose you to calculate difference spectra to see more information. It is necessary to analyse more bands. Next, the spectral band parameters (such as position, peak height, and band area) can be calculated to see what exactly processes undergoing at the molecular level.
You can also see https://doi.org/10.1016/j.saa.2017.07.001
maybe it’ll help you.
Thank you all for your answers, I think I have found a good explanation of the change of intensity as temperature increase. I found that a higher intensity of absorption in the region of hydroxyl group indicates an increase of the hydroxyl number in the polyol.
However, in the case of my samples prepared under argon atmosphere and then also nitrogen, the sample heated at the lowest temperature (121°C) showed the highest transmittance in the region -OH, even higher as the one obtained for the reference (unheated sample). I don't know if this change is related to a smaller amount of sample and/or pressure used in the measurement. What do you think?
Krzysztof Beć I didn't weigh the sample before measured it in FT-IR. I tried though, to put more or less the same amount, so the difference would be quite small.
I've been told that a smaller amount of sample could have those effects on the results (different peak intensities as it shown in the attached last picture). In my case, I registered a melting point of 119°C for erythritol.
Please look at the following below links which may help you in your analysis:
http://www3.uma.pt/jrodrigues/disciplinas/QINO-II/Teorica/IR.pdf
http://cdn.intechopen.com/pdfs/37067/InTech%5BHYPHEN%5DFourier_transform_infrared_spectroscopy_for_natural_fibres.pdf
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2701167/pdf/aci-3-135.pdf
Thanks
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