The Advantages of FTIRs

To be able to compare different types of spectrometers to each other we need a measure of spectral quality. One common measure is called the signal-to-noise ratio of a peak, or SNR for short. SNR is defined by Equation 1.8. 

FIGURE 1.8 How to measure signal and noise to calculate a signal-to-noise ratio (SNR). In this example the SNR is (0.0215)/(0.00244) = 9. 

FIGURE 1.9 An example of a spectrum with a good SNR. The PPN is 0.001, so the portions of the spectrum above 0.1, as denoted by the dashed line, have a signal-to-noise ratio of greater than 100. 

The spectrum in this figure (an ATR spectrum of the author s thumb) has a PPN of 0.01, so the regions of this spectrum with an absorbance of less than 0.1, as denoted by the dashed line, have an SNR of less than 10. Note there is noise clearly visible in this spectrum as fuzz in the baseline. Also, the spectrum has a sloping baseline and a CO2 artifact peak near 2350 cm This is an example of a poor spectrum, and changes in sampling or scanning conditions should be pursued to try and improve its quality. 

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The advantages of FTIR over the dispersive technique are 1) it is faster, making it possible to be incorporated into chromatography schemes, as will be seen in Chapters 12 and 13, and 2) the energy reaching the detector is much greater, thus increasing the sensitivity. 

Practical Aspects of Operation the Advantages of FTIR-based Analyzers... 

List the advantages of FTIR over dispersive IR spectroscopy. 

Because of the advantages of FTIR spectrometers and their broad availability, attempts have also been made to perform polarization measurements on such spectrometers. An experimental setup for polarization modulated Fourier transform in-... 

In the identification of different polymorphs in polymers the FTIR technique presents, with respect to the diffraction techniques, the advantage of easier and more rapid measurements. In particular, the high speed of the measurements allows to study the polymorphic behavior under dynamic conditions. As an example let us recall the study of the transition from the a toward the P form of PBT induced by tensile stresses, evaluated by quantitative analysis of the infrared spectra [83],... 

The FTIR technique has also the advantage of being easily associated to other techniques. For instance, the FTIR microscopy, which couples the visible image of the samples to the corresponding infrared spectra, allows the selection of microareas of interest, and thus an easy determination of the crystalline forms corresponding to different regions, in samples in which more than one polymorph is present [103]. 

The photoacoustic effect was first discovered by Alexander Graham Bell in the early 1880s [18], but it was not applied to Fourier transform infrared (FTIR) spectroscopy until a century later [19,20], Significant advantages of FTIR photoacoustic spectroscopy (PAS) include the following (1) Spectra may be... 

Infrared Spectroscopy. The use of IR (9.10.11.12) and FTIR (3.4) for coal mineralogy has been reported. Painter and coworkers (3) demonstrated that FTIR can provide a virtually complete analysis. Painter, Brown and Elliott (4), and others (9.10.11) discuss sample preparation, reference minerals, and data analysis. The advantages of IR are 1) high sensitivity to molecular structure, 2) unequivocal identification of a number of minerals, 3) small sample size (a few milligrams), and 4) rapid analysis time (once LTA is available). Disadvantages include 1) reliance on reference minerals, 2) requires careful attention to sample preparation, and 3) limited selectivity (discrimination among similar minerals). 

Fourier-transform infrared (FTIR) spectrometers encode infrared wavenumbers by moving a mirror in a Michelson interferometer which results in a unique, path-dependent pattern of interference for each light wavelength in the IR beam. FTIRs have come to totally dominate the IR market and are the means by which most of the work described in this review was accomplished. Only for some special applications (modulation spectra and time-dependence studies) are dispersive-based (scanning monochromator or tuned laser) spectrometers still used. The advantages of the FTIR approach are that the entire spectral region of interest can... 

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