ABSTRACT
While in the ‘‘old days,’’ samples in a solid or liquid state were measured by dispersive working instruments, the 1980s brought a renaissance of IR spectroscopy through the introduction of the Fourier transform (FT) technique. While the former dispersive instruments contained a monochromator which provided one welldefined wavelength range after the other to which the sample was exposed, FT-IR instruments irradiate the sample with an interference wave produced in an interferometer. The interferogram recorded by the detector is related to the spectrum through its Fourier transform. The fact that the radiation reaching the detector contains all wavelengths at one time gives the so-called multiplex (or Fellgett) advantage. It allows spectra of the same signal-tonoise ratio (SNR) to bemeasuredmuch faster on an FT-IR spectrometer than on a traditional dispersive instrument. Another outstanding advantage is given by the optical throughput (Jacquinot advantage), which is greater for an interferometer than for a monochromator. The invention of the Fourier transform infrared (FT-IR) technique opened up new possibilities in instrumentation and in the coupling of analytical systems as well as in the application
Figure 1 The static FT-IR spectrum of a spruce dissolving pulp cellulose together with an overview of the band assignments.
