Can anyone explain to me about why there is a difference between dye powder and aqueous dye solution (1000 ppm) in FTIR spectra? Why the peaks in aqueous dye solution of FTIR spectrum is lesser than the dye powder FTIR spectrum which has only 2 peaks appeared in dye solution FTIR spectrum?
Thank you.
The -OH absorption bands of water are too strong and suppress anything else (thats the 2 peaks in the lower spectrum). Normally it is not possible to analyse components dissolved in aqueous solutions with FTIR for that reason. Of course, it depends on concentration.
Thomas is correct - to have any hope of measuring in aqueous solution, you need to significantly increase your concentration. Even then, you will see changes in FTIR modes in the slid form because of intermolecular coupling.
"Improved Protocols for Vibrational spectroscopic analysis of body fluids",
Franck Bonnier, François Petitjean, Matthew J. Baker, Hugh J. Byrne,
Journal of Biophotonics, 7, 167-179 (2014)
In general spectra of materials in solution have fewer and broader bands than the solids, particularly if the material is crystalline. Not a comparison I'd recommend when looking for trends in the performance of your material.
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