Fast Fourier transform infrared

Fast Fourier Transformed Infrared Spectroscopy (FTIR)... 

Fast Fourier Transformation is widely used in many fields of science, among them chemoractrics. The Fast Fourier Transformation (FFT) algorithm transforms the data from the "wavelength" domain into the "frequency" domain. The method is almost compulsorily used in spectral analysis, e, g., when near-infrared spectroscopy data arc employed as independent variables. Next, the spectral model is built between the responses and the Fourier coefficients of the transformation, which substitute the original Y-matrix. 

As mentioned, we also carried out IR studies (a fast vibrational spectroscopy) early in our work on carbocations. In our studies of the norbornyl cation we obtained Raman spectra as well, although at the time it was not possible to theoretically calculate the spectra. Comparison with model compounds (the 2-norbornyl system and nortri-cyclane, respectively) indicated the symmetrical, bridged nature of the ion. In recent years, Sunko and Schleyer were able, using the since-developed Fourier transform-infrared (FT-IR) method, to obtain the spectrum of the norbornyl cation and to compare it with the theoretically calculated one. Again, it was rewarding that their data were in excellent accord with our earlier work. 

An important tool for the fast characterization of intermediates and products in solution-phase synthesis are vibrational spectroscopic techniques such as Fourier transform infrared (FTIR) or Raman spectroscopy. These concepts have also been successfully applied to solid-phase organic chemistry. A single bead often suffices to acquire vibrational spectra that allow for qualitative and quantitative analysis of reaction products,3 reaction kinetics,4 or for decoding combinatorial libraries.5... 

Other combinations of chromatography techniques with MS which may be useful in environmental studies are the coupling of high performance liquid chromatography (LC) with MS [84,384,504,506,530,585-593],LC with MS-MS [181, 594 - 599], LC with atmospheric pressure chemical ionization MS (LC-APCI-MS) [600], and Fourier transform infrared spectroscopy-fast atom bombardment coupled to LC-MS (FTIR-FAB-LC-MS) [514]. 

Application of nLFP techniques in the IR region has been available for well over a decade. In one approach, laser diodes are used to generate the monitoring beam and a fast IR detector employed. Alternatively, a step-scan spectrometer uses the same methodologies employed by normal Fourier transform infrared (FTIR) spectrometers, but spectral capture is much faster. 

Since the article by Spedding1 on infrared spectroscopy and carbohydrate chemistry was published in this Series in 1964, important advances in both infrared and Raman spectroscopy have been achieved. The discovery2 of the fast Fourier transform (f.F.t.) algorithm in 1965 revitalized the field of infrared spectroscopy. The use of the f.F.t., and the introduction of efficient minicomputers, permitted the development of a new generation of infrared instruments called Fourier-transform infrared (F.t.-i.r.) spectrophotometers. The development of F.t.-i.r. spectroscopy resulted in the setting up of the software necessary to undertake signal averaging, and perform the mathematical manipulation of the spectral data in order to extract the maximum of information from the spectra.3... 

Several major points should be mentioned. In FT-IR interferograms are recorded, and the infrared spectra computed from the interferograms, via a fast Fourier transform algorithm introduced relatively recently (4). It is tire replacement of the monochromator of earlier spectrometers by an interferometer which is primarily responsible for the improved performance of FT instruments. 

In Fourier transform infrared (FTIR) spectroscopy, simply one beam is used during the IR analysis of a sample, that is, in this case, all frequencies go through the instrument at one time [61] (see Figure 4.18). The method is called FTIR spectroscopy, because a Fourier transformation is carried out by a computer in order to work out the obtained data and yield a spectrum. FTIR is fast, that is, a spectrum can be obtained in less than a second. Besides, it is a very sensitive technique, because it is possible to make as many scans as necessary to obtain a good spectrum. 

It is unreahstic to attempt the use of the Fourier series or of the Fourier integral transforms without the aid of a computer. In recent years a fast Fourier transform (FFT) algorithm for computers has become widely used. This is particularly useful in certain kinds of chemical instrumentation, specifically nuclear magnetic resonance and infrared absorption spectrometers. In such instruments the experimental observations are obtained directly in the form of a Fourier transform of the desired spectrum a computer that is built into the instrument performs the FFT and yields the spectrum (see Chapter XIX). 

Fourier transform infrared reflectance spectrum (FTIR) results indicate that AChE was immobilized successfully on the MWCNT/PDDA surface. CV results show that electrooxidation of thiocholine occurs at a much lower oxidation potential +0.55 V at MWCNT/GCE and the electrooxidation current is ten times higher than that of bare GCE. In addition, amperometric results show that the response of thiocholine at MWCNT/GCE was 200 times more than that of bare GCE. This significant enhancement in the anodic oxidation current of the enzymatic product thiocholine can be attributed to the fast electron transfer and... 

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