Does anyone know what could be the reason why my FTIR spectrum shows peaks only at a low wavelength (under 500 cm-1)? I did it for 4 different samples (polymer, protein and two types of nanoparticles) and all of them didn't show any peaks in the region which could be significant.
have you run a standard sample to make sure the instrument is functioning properly?
for transmission, the usual standard is a polystyrene film.
other sampling methods (atr, diffuse reflectance) can use different standards.
if the standard looks correct, you probably do not have enough sample to get good signal.
I would go with the contamination of the device, maybe with some polymers as well. Does the spectrometer run a background spectrum before any analysis? If yes, and the contamination is there, then the software would cut out the peaks coming from it and on your sample you wont get these peaks as well.
Could you share the spectra with us? I agree with James E Hanson that the instrument performance should be verified first. Another possible cause of your troubles: if you have an older IR source, the short wavenumber intensities die first (below ca 600 cm-1 for our FTIR by Bruker, but I guess it will be similar for other brands). The low signal may produce a significant error while applying the background subtraction. What happens if you cut off the measurement at 600 cm-1 and rescale it? Do you get a proper spectrum, then?
If the FTIR spectrum of your sample shows peaks only at low wavelengths (under 500 cm^-1), it is likely that your sample contains compounds with low-frequency vibrational modes. These low-frequency modes are often associated with the vibrations of heavy atoms, such as metals or halogens, or with large organic molecules, such as polymers or proteins.
In some cases, the low-frequency region of the FTIR spectrum can be obscured by water vapor, which has strong absorption bands in this region. To minimize the interference of water vapor, it is important to ensure that the sample is completely dry and that the FTIR instrument is properly purged with dry air or nitrogen.
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