What would cause the peaks in a IR analysis to be smaller than they should be? My sample had the right peaks where they should be and they were the right shape but were shorter then they should be.
Something different is what the y axis says on the IR analysis that they gave us so we would know how the IR was supposed to look for our samples. But the y axis on the one they gave us said "percent transmittance" while the IR graph had "percent reflectance". Not sure if it's the same.
If they are though then an example of the difference in peak size is:
my sample of 4-bromo-2-chloroacetaniilide
1 middle sized peak: 3275.24 cm-1
and the intensity was : 69.608 % reflectance
The given IR card showed the peak going all the way down to about 30% percent transmitance ( I don't have the exact value)
Thank you.
Something different is what the y axis says on the IR analysis that they gave us so we would know how the IR was supposed to look for our samples. But the y axis on the one they gave us said "percent transmittance" while the IR graph Ihad "percent reflectance". Not sure if it's the same.
The only explanation I might offer is that you may have performed an ATR (attenuated total reflectance) but I haven't had experience with that instrument. .
Oh..yes I did perform an ATR. I didn't think it was that different from a normal IR but I guess it is from what your saying.
Thank you Dr.Bob
I don't know that it's different. I've not used one.
Well, you don't need solvent and you just use the sample as is.
The difference in peak size between your sample and the given IR card could be due to a few possible reasons:
1. Sample concentration: If the concentration of your sample is different from the reference sample used on the IR card, it can result in variations in peak intensities. Higher concentrations of the sample may cause broader and taller peaks, while lower concentrations can result in smaller peaks.
2. Instrument settings: The IR instrument settings, such as the gain or sensitivity, can affect the intensities of the peaks. If the instrument settings were different when analyzing your sample compared to the reference sample, it can lead to variations in peak sizes.
3. Measurement technique: The difference between "percent reflectance" and "percent transmittance" could also contribute to the discrepancy in peak size. In IR spectroscopy, "percent transmittance" is typically used to measure the amount of infrared light passing through the sample, while "percent reflectance" refers to the amount of infrared light reflected off the sample surface. These values are not necessarily equivalent and could account for the difference in peak size between your sample and the reference IR card.
To troubleshoot these issues and obtain more accurate peak sizes, you can consider the following steps:
1. Confirm the concentration: Ensure that your sample is prepared at the correct concentration and that it matches the reference sample used on the IR card. If necessary, adjust the concentration to align with the reference sample.
2. Optimize instrument settings: Check the instrument settings used for your sample analysis, such as gain or sensitivity. Consult the instrument manual or contact the manufacturer for guidance on the appropriate settings for your specific analysis.
3. Verify measurement technique: If possible, check if the instrument is capable of measuring both transmittance and reflectance and determine which technique was used for the reference IR card. If the techniques differ, it may not be possible to directly compare the peak sizes.
4. Consult an expert: If the discrepancies persist and you require accurate peak sizes for your analysis, consider consulting an expert in IR spectroscopy or the manufacturer of the instrument for further guidance and troubleshooting.
Remember, obtaining accurate and reproducible IR spectra might require careful attention to sample preparation, instrument settings, and measurement technique.