I'm using FTIR-ATR to measure the IR of a polymer film. When I use low pressure, I get one spectra and when I use high-pressure, I get another spectra. The question is that the spectra with the higher intensity peaks is the one with the low pressure, that contradicts everything in the literature. Can it be that the ATR tower has some king of pressure problem?
Hello
If the polymer is very soft it can squeeze out when yoy aply a high pressure and you will scan a very thin sample and therefore you get low intensity spectrum. In this case is better to go with low to moderate pressure.
Hello Arjun,
Typically, when you press the sample more, higher concentrations will be detected by FTIR and you will see higher intensity peaks. However, as Redouane mentioned, if your sample is too soft you may squeeze the sample out of the detection area and thus you will read less concentrations in your sample.
Few recommendations,
1- You may need to try normalization techniques, where you basically choose a wavenumber that corresponds to one peak that is not affected by your treatment and then normalize all your samples to have same peak intensity at the chosen wavenumber. This technique will eliminate variability that may be caused by variations in the applied pressure.
2- Try to stay as consistent as possible. I would choose the pressure that will lead to higher intensity peaks and stick to it all the time. This will lead to higher signal to noise ratio and it will increase your ability to detect small differences between different treatments.
3- You may try to adjust the testing gap to prevent squeezing of the sample or you may even try liquid cell FTIR if it is available in your lab.
Best regards,
Michael
You didn't mention whether, upon complete removal of the film from the internal reflection element, whether you can obtain a spectrum of a contaminant which has been transferred from the sample to the surface of the IRE. There are clamps, etc. available that can help with setting reproducible pressures on soft samples. See
http://www.harricksci.com/
Dear Arjun Radha Krishna
If your film is self-supporting (is not fixed to a substrate) and reasonably thin, you can easily measure it normaly in transmitance mode. We used this approach to measure IR spectra of polysaccharide films with 20 micron thickness and it worked very well.
Regards
Josef
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