Question

List the one main instrumental difference between a dispersive IR spectrometer and an FTIR spectrometer. What advantage does this give the FTIR over the dispersive IR? (4pts)

Answer 1

Dispersive IR spectroscopy and FTIR spectroscopy:

They both produce spectra . Dispersive IR spectroscopy is grating spectroscopy. It gives spectra of different 'orders' directly. FTIR requires processing for indirect way to get spectra . IR ranges from 2.5 micrometer to 15 micrometer in electromagnetic spectrum .IR detectors consists of a semiconductor such as PbS or liquid nitrogen cooled HgCdTe( MCT) . Dispersive IR spectrometer use a diffraction grating in monochrometer to disperse the different wavelengths of light . Dispersive IR spectrometer have largly been replaced with FTIR spectrometer.FTIR is spectroscopic technique . It can produce an interferrogram in within a second.

Advantages of FTIR over IR spectroscopy:

More energy reaches the sample and hence the detector in FTIR than in IR spectrometer. Signal -to-noise ratio of an IR spectrometer measured on an FTIR is higher than signal to noise ratio attained on a dispersive Interferometer .

Many scans can be completed and combined on an FTIR in a shorter time than one scan in a dispersive instrument.FTIR has faster data collection.Major advantage is speed, reproducibility and easy automation .But more sensitivity of FTIR can be disadvantage sometimes.