FTIR Tutorial
- To remove the background from our spectrum: Click Math-->Ratio.
- Then click OK to select "Disk File" as the reference source.
- Then load the background file we just measured (it
will be the same name as the sample, with a .bkg
extension).
You should then have a transmittance file (.ras) extension. This has the units of %transmittance -with the absorbance bands pointing downwards. A transmittance spectrum of PS is shown below.
- This spectrum shows INTERFERENCE FRINGES - the
waviness seen above 3100 cm-1. These are
caused by the IR beam bouncing inside the PS film. Your spectrum may not
show these. Incidentally, they may be used to calculate the thickness of
your film, if present!
- You can see that this spectrum covers the range
between about 5 and 80% transmission. This is ideal. If you have too
thick a sample, or the IRIS is open too far, the peaks will appear
'blunted', and reach 0% transmission, in this case you must decrease the
IRIS, or use a thinner sample.
- On the other hand, too small an IRIS setting, or too thin a sample will lead to small peaks, and therefore low S/N.
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If you save your spectrum now, it will have the extension .ras. There is another way to display the spectrum, as an absorbance spectrum . Convert your spectrum to an absorbance spectrum by clicking math-->Convert-->Absorbance, or the convert button on the toolbar, shown on the left. |
The absorbance spectrum is shown in the next page.