"Advantages and disadvantages of Fourier Transform spectrometric techniques compared to traditional analytical methods
In a dispersive spectrometer, wavenumbers are observed sequentially. In an FT-IR and FT-NIR spectrometer, all the wavenumbers of light are observed simultaneously. Therefore, when spectra are collected under identical conditions the signal-to-noise (S/N) ratio of the FT-IR spectrum will be greater than that of the dispersive IR spectrum (HILL et al. 1997).
In FT-IR instruments there is no need to limit the beam width in order to obtain an adequate resolution. In fact, a circular optical aperture is used in FT instruments, and the beam area is 75 to 100 times larger than the slit area of dispersive instruments (SETTLE 1997). As a consequence, there is an advantage of increased beam intensity going through the sample and therefore a much higher throughput with a FT-IR than with a dispersive instrument (JACQUINOT 1984).
High and constant resolution: Spectral resolution is a measure of how well a spectrometer can distinguish closely spaced spectral features. Filter instruments cannot offer high resolution because, in dispersive instruments, resolution decreases as lower frequencies are scanned. In FT-IR, the resolution depends on the optical path difference (OPD) that can be achieved. Thus it is constant across the scanning range (WILKS 1986, PERKINS 1987)."
(Near Infrared spectroscopy, a quality control tool for the different steps in the manufacture of
herbal medicinal products
Magali Laasonen nÈe Grata
ACADEMIC DISSERTATION
Division of Pharmacognosy
Department of Pharmacy
Faculty of Science
University of Helsinki
HELSINKI 2003)
"Two important parameters to ensure good spectra collection of a FT-NIR spectrometer during an analysis are number of scans and resolution. Resolution in an FT-NIR determines a small frequency interval that can be distinguished over a spectral range and typically this parameter ranges from 4 and 64cm-1. In case of selecting a high resolution, the spectrum becomes more detailed, but it captures more noise and the analysis takes a longer time. The number of scans acquired enhances the signal amplitude per unit time. This parameter is inversely proportional to noise effect, and the typical values of number of scans are between 16 and 128 (PLSplus IQ user’s guide; Thermo Electron Corporation, Salem, NH, USA). Setting these parameters is based on a compromise between the operation time and analysis quality desired."
(FT-NIR spectroscopy and Laser Diffraction particle sizing of
APIs in Pharmaceutical formulations, Joana Lúcia Carrilho Figueiredo
Dissertação para obtenção do Grau de Mestre em
Mestrado Integrado em Engenharia Química, Setembro de 2008)
"Each spectrum had an average of 64 scans and provided a resolution
of 16cm-1. The spectral data analysis covered the range from 3996.2 to 12004 cm-1
. "
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