What is Fourier Transform infrared spectroscopy?
Fourier Transform infrared spectroscopy (FTIR) is a method for obtaining an IR spectrum by irradiating the sample with all IR frequencies at once.
In ordinary IR spectroscopy, we irradiate the sample with monochromatic light and measure the absorption at each frequency in turn.
In FTIR, we irradiate the sample with the all the frequencies at the same time.
The heart of the machine is a device called an interferometer, which splits the light into two beams, one of which is reflected from a fixed mirror and the second from a sliding mirror.
The beams are recombined and passed through the sample.
The differing path lengths cause the two beams to interfere with each other when they are combined, so the detector receives a complex signal that also includes all ihe IR absorptions.
A computer uses a mathematical process called a Fourier transform to work backwards from the signal and calculate what the absorption is at each frequency.
It then creates a plot that looks like an ordinary IR spectrum.