I have conducted an FTIR analysis for my extracted asphaltene but I noticed that the absorbance level in the sample is starting from 40% not 0% which means that every single wavelength was absorbed by the sample for at least 40% , do anyone has any explanation for this ?
Note: the FTIR result is attached
What is the resolution?
Did you checked/corrected the background?
regards,
GB
Actually this is a transmittance spectrum. I guess you used a KBr pellet, right?
It is important that your sample is homogeneous. An inhomogeneous sample can have areas of high transparency, and areas of high absorbance. The result can be a high, non zero absorbance (non 100% Transmission) baseline, and relatively low absorbance peaks.
another reason for a depressed baseline (in %T, elevated baseline in Abs) with FTIR, could be the presence of some material that has a broad absorbance across the full spectral region.
Carbonaceous materials, such as soot can definitely cause this sort of spectral artefact.
could there be soot in your sample? Asphaltenes are known to form soot under pyrolysis conditions....
It appears that you used very wet KBr power to make a KBr pellet. Your KBr pellet must have been translucent (white and hazy), rather than completely transparent. This causes scattering of the IR radiation especially at the shorter wavelength (larger wavenumber side), leading to the sloped baseline and lower transmittance. Do the following.
1. Keep a small amount of KBr powder in a desiccator with a large amount of drying agent, such as well dried silica gel and others. Keep the KBr bottle open in the desiccator and leave it there for minimum of 1 week. This drying process is very important.
2. When you want to use the KBr powder, do not keep it exposed to air for a long time as the atmospheric moisture will be absorbed. Measure 250-300 mg of KBr powder. Measure 1 mg or less of your sample. Do not add too much sample as the KBr pellet will not be transparent.
3. Mix your sample and part of KBr powder (1/5 of the measured KBr powder) and grind the mixture very well (quickly before the moisture reabsorb). This part of KBr powder is used as a grinding aid.
4. After grinding, add the remaining 4/5 of the KBr powder. Mix the ground powder and unground KBr powder. Do not grind this mixture (this procedure is very important to avoid water absorption), but gently mix it till homogeneous. The ground KBr exposes a fresh KBr crystal surface that has very high energy and adsorbs atmospheric water in a large quantity.
5. Press the mixture in the KBr pellet press for 2 min, release the pressure and rotate the KBr pellet maker by 180o and press it again without the vacuum for additional 2 min. You should have very transparent pellet and the baseline should not be tilted and start with much higher transmittance.
Hatsuo Ishida thanks a lot for this detailed procedure !
For sure i will try it thanks a lot, really appreciated.
Aregato Kuzaimas
It is normal, whene there are no moleculare stimulate in this regine
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