Step 2: The second step is getting a background spectrum by collecting an interferogram and its subsequent conversion to frequency data by inverse Fourier transform. We obtain the background spectrum because the solvent in which we place our sample will have traces of dissolved gases as well as solvent molecules that contribute information that are not our sample. The background spectrum will contain information about the species of gases and solvent molecules, which may then be subtracted away from our sample spectrum in order to gain information about just the sample. Figure 6 shows an example of an FTIR background spectrum.
fig8 background IR spectra.JPG
Figure 6. Background IR spectrum
The background spectrum also takes into account several other factors related to the instrument performance, which includes information about the source, interferometer, detector, and the contribution of ambient water (note the two irregular groups of lines at about 3600 cm–1 and about 1600 cm–1 in Figure 6) and carbon dioxide (note the doublet at 2360 cm–1 and sharp spike at 667 cm–1 in Figure 6) present in the optical bench