The image attached includes FT-IR spectrum of gelatin and sodium hydrogen carbonate mixture; the peak in the magnified region are source of question for us.
For me this is a peak from CO2 and its results from measuring conditions
Check in free NIST database. Generally each program used to FTIR data acquisition has a possibility to compensation CO2 and water. Try to find this option.
I agree with the previous comments, a peak coming from CO2 not enough compensated. Check also the conditions of detection for the background spectrum
I agree with previous comments. The best way is to perform a background immediately before the spectral acquisition to get a good compensation for C02, apart from that purging is also an option.
This is indeed a CO2 spectrum. Purging is the best solution. Quick background before scan is the fastest solution. Breathing near the sample does not help. To convince yourself it is CO2, get a background spectrum, breath near the sample sample and the CO2 band will increase in intensity.
This is similar to a hygroscopic compound absorbing moisture.
Your added carbonate does not show up in the spectrum as the film may be to thick.
It is a reflection IR or transmission? What is the thickness of your film?
You can deposit an ultrathin film on a Ge crystal and perform ATR with it. You may find what you are looking for.
I agree, this is CO2. I would expect carbonate to appear at a much lower wavenumber than CO2 (main band at (very roughly) ~1400 cm-1)
I have a few other comments for your spectra, hope it will be helpful in your future measurements. From your spectrum, it looks like you have measured this using a diamond ATR. I can see this based on remains of the diamond band (especially the blue spectrum) which should not be there. Make sure that you are not over-saturating your detector (too much signal). Also your green spectrum has an overall lower absorbance than the others (assuming you have not scaled the spectra). If you are using ATR, it is important to make sure that you have good contact between your sample and the ATR element (the diamond) because this will strongly affect the absorbance of you spectrum.
To add to Andrew's comments, different pressures on the ATR crystal will also produce diamond artifact bands. Generally this isn't a problem unless you are looking for weak nitrile bands.
I also think the peak is due to CO2. I have noticed such peaks after performing CO2 corrosion inhibition analysis for X60 steel in CO2-saturated NACE brine solution. You may also confirm this with the noticeable peak around 666cm-1
I also observed a similar peak in Halloysite nanocrystals and it was concluded that it CO2 peak
The same peak was observed with green synthesized iron oxide nanoparticles
On case of ATR-FTIR, environment should be made before the sample. If done, CO2 should be subtracted and no peak of CO2 appears. @Michalina Kotyczka-Morańska
If anyone has a research paper for CO2 peak around (2300 - 2400 Cm-1), please share it.
Article FTIR–PAS: A powerful tool for characterising the chemical co...
Characterization of microalgal species through TGA/FTIR analysis: Application to nannochloropsis sp.
These articles may be useful
The Group O=C=O stretching (carbon dioxide)
The Frequency Range 2400-2000 cm-1 when Absorption ( 2349 cm-1)Appearance strong
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