FTIR
/ ef-tee-eye-AR /
FTIR is a clever way to record an entire infrared spectrum all at once instead of one color at a time. The old approach scanned slowly through each frequency, like checking the pitch of a piano one key after another. FTIR instead lets the whole chord sound together, records the blended signal, and then uses math to untangle which notes were in it.
More precisely, an FTIR instrument passes infrared light through a moving-mirror device called an interferometer, producing a tangled signal called an interferogram. A mathematical operation, the Fourier transform, converts that interferogram into the familiar plot of absorption versus wavenumber.
It matters because measuring all frequencies simultaneously makes FTIR fast, sensitive, and able to average many scans for a clean result — which is why nearly every modern infrared spectrometer is an FTIR. The honest caveat is that the spectrum you see is computed, not directly observed, so good results depend on proper calibration and a clean background scan.
A technician drops a flake of unknown plastic on an FTIR's sampling crystal and presses scan. In seconds the interferometer collects the data, the software runs the Fourier transform, and a library match identifies the plastic as polyethylene.
FTIR records all infrared frequencies at once, then computes the spectrum.
FTIR is not a different kind of infrared spectroscopy — it produces the same kind of spectrum as the old scanning instruments, just faster and with less noise. The "FT" describes how the data are collected, not what is measured.