A small chart on the basic differences between them

1. PROPERTIES DISPERSIVE IR FTIR
1.Components Many moving parts result in
mechanical slippage.
Only mirror moves during an experiment
2.Calibration Calibration against reference spectra
required to measure frequency
Use of laser provides high frequency precision (to 0.01
cm-1 (Connes’ advantage)
1.Stray light Stray light within instrument causes
spurious readings
Stray light does not affect detector, since all signals are
modulated.
2.Resolution In order to improve resolution, only
small amount of IR beam is allowed to
pass through the slits.
Much larger beam aperture used; higher energy
throughput (Throughput or Jacquinot’s advantage).
3.No. of
Frequency
Only narrow-frequency radiation falls
on the detector at any one time.
All frequencies of radiation fall on detector
simultaneously; improved S/N obtained quickly
(Multiplex or Fellgett’s advantage)
4.Scan speed Slow scan speeds make dispersive
instruments too slow for monitoring
systems undergoing rapid change (e.g.
GC effluents)
Rapid scan speeds permit monitoring samples
undergoing rapid change.
5.Source
effects
Sample subject to thermal effects from
the source due to length of scan time.
Short scan times, hence sample is not subject to thermal
effects.
6. IR from
sample itself
Any emission of IR radiation by sample
will fall on detector due to the
conventional positioning of the sample
before the monochromator.
Any emission of IR radiation by the sample will not be
detected.
7.Advantage
of Beam
optics
Double beam optics permit continuous
real-time background substraction.
Single beam optics; background spectrum collected
separately in time from sample spectrum.
Can result in error if background spectra not collected
frequently.