Instrumentation

Single-beam Fourier Transform IR spectrometer

Following the diagram from the Source coil to the IR detector, the parts of the Fourier Transform IR (FTIR) spectrometer will be explained.

Source Coil--The infrared light source. This is where the IR spectrum, of which the the instrument is capable, is produced.

Fixed Toroidal Windows--Fancy name for curved pieces of glass that completely reflects and focuses the light in a new direction. For example, the first Fixed Toroidal Window aims the source at the Beam Splitter.

Interferometer--Chooses to wavenumber to be scanned. The beam splitter splits the source into 50%. Half of the light gets sent to the scan mirrors to be changed into a specific wavenumber. Then both the the changed light and the unchanged light meet again at the beam splitter to have half of the change and half of the unchanged light go on to the sample.

Laser Fringe Detector--This works in conjunction with both the source coil and the HeNe laser. This helps focus the IR beam. This is set at a zero value when only the HeNe laser is focused on it. If some of the light from the Source Coil drifts onto the detector, the interferometer changes the focus so this is set at zero again.

Adjustable Toroidal Window--This reflects and focuses the light towards the sample. It is adjustable to compensate for the focusing of the interferometer.

KBr windows--These allow the IR light to test the sample without being absorbed. This is the same reason KBr is used to make solid samples plates.

Sample Area--Where your solid, liquid or gas sample goes.

Purge Cover--IR spectrometer work better with less air. Usually, the instrument is purged with nitrogen to remove the air.

IR Detector--The detector works by recording differences in the intensity of light that comes through to it. It is initially set at a zero value. It does not know what wavenumber is being scanned. However, combining the information from the interferometer with the intensity information of the IR detector, a spectrum is created.