Fourier-transform infrared spectrometers

A Michelson interferometer is generally the device used in an FTIR spectrometer. The Michelson interferometer is composed of two mirrors and a beam splitter positioned at an angle of 45° to the fixed and moving mirrors. 

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Fig. 19.3 Layout of a Fourier-transform infrared spectrometer. Reproduced by permission of Lloyd Instruments PLC, Warsash, Southampton S03 6HP.

Co concentration was determined by spectrophotometer (Varian Cary 500) at 692 nm wave length, with the sample diluted with a 9 mol/L concentrated HCl solution. NO content in gas phase was obtained by an on-line Fourier transform infrared spectrometer (Nicolet E.S.P. 460 FT-IR) equipped with a gas cell and a quantitative package, Quant Pad. 

The basic methods of the identification and study of matrix-isolated intermediates are infrared (IR), ultraviolet-visible (UV-vis), Raman and electron spin resonance (esr) spectroscopy. The most widely used is IR spectroscopy, which has some significant advantages. One of them is its high information content, and the other lies in the absence of overlapping bands in matrix IR spectra because the peaks are very narrow (about 1 cm ), due to the low temperature and the absence of rotation and interaction between molecules in the matrix. This fact allows the identification of practically all the compounds present, even in multicomponent reaetion mixtures, and the determination of vibrational frequencies of molecules with high accuracy (up to 0.01 cm when Fourier transform infrared spectrometers are used). 

For infrared spectroscopy, 20-50 mg of the cobalt-exchanged zeolite was pressed into a self-supporting wafer and placed into an infrared cell similar to that described by Joly et al. [21], Spectra were recorded on a Digilab FTS-50 Fourier-transform infrared spectrometer at a resolution of 4 cm-i. Typically, 64 or 256 scans were coadded to obtain a good signal-to-noise ratio. A reference spectrum of Co-ZSM-5 in He taken at the same temperature was subtracted from each spectrum. 

The infrared spectra of the different samples were taken with a Fourier Transform infrared spectrometer (Digilab FTS-14) using the double beam mode vs. air as reference. 150 scans per sample and 100 scans per reference, at a resolution of 4 cm-l, were taken for every sample. All spectra were stored on tape, and a digital substraction of the after- and- before UV exposure (or any other sample treatment) spectra was performed, whenever needed, by an on-line computer, thus permitting a better visualization of the spectral changes in the polymer by UV- photooxidation. 

The pyrolysis of wood, oxygen chemisorption and oxidation of wood chars were carried out in a computerized coupled TG-FTIR system containing Cahn-R-100 electric balance, DuPont Model 990 thermal analyzer and Nicolet MX-1 Fourier transform infrared spectrometer. All of these sequential processes are carried out within the thermal balance without interruption. 

Transmission infrared spectra of species adsorbed on the catalyst were taken with a Digilab FTS-10M Fourier-transform infrared spectrometer, using a resolution of 4 cm-l. To improve the signal-to-noise ratio, between 10 and 100 interferograms were co-added. Spectra of the catalyst taken following reduction in H2 were subtracted from spectra taken in the presence of NO to eliminate the spectrum of the support. Because of the very short optical path through the gas in the reactor and the low NO partial pressures used in these studies, the spectrum of gas-phase NO was extremely weak and did not interfere with the observation of the spectrum of adsorbed species. 

Fourier transform infrared spectrometers encounter none of the stray light problems usually associated with dispersive spectrometers. 

Olsen, E. Serially interfaced gas chromatography/Fourier Transform infrared spectrometer/ion trap detector. Finnigan MAT IDT 35. 

We discussed the fundamentals of mass spectrometry in Chapter 10 and infrared spectrometry in Chapter 8. The quadrupole mass spectrometer and the Fourier transform infrared spectrometer have been adapted to and used with GC equipment as detectors with great success. Gas chromatography-mass spectrometry (GC-MS) and gas chromatography-infrared spectrometry (GC-IR) are very powerful tools for qualitative analysis in GC because not only do they give retention time information, but, due to their inherent speed, they are also able to measure and record the mass spectrum or infrared (IR) spectrum of the individual sample components as they elute from the GC column. It is like taking a photograph of each component as it elutes. See Figure 12.14. Coupled with the computer banks of mass and IR spectra, a component s identity is an easy chore for such a detector. It seems the only real... 

The signal to noise ratio is limited in any physical intensity measurement, however, by the statistical fluctuations in the photon flux (photon shot noise). This limit can be reached with Fourier transform infrared spectrometers. 

XANES and EXAFS were conducted at BL-lOB in the Photon Factory of the National Laboratory for High Energy Physics (KEK-PF)[12]. s Fe Nttssbauer spectra were recorded with a Shimadzu MEG-2 spectrometer(13]. Isomer shifts were given relative to a-Fe. Infrared spectra were recorded by a Shimadzu Fourier-transform infrared spectrometer(FTIR-4100) with a resolution of 2 cm i. Diffuse reflectance UV-VIS spectra were obtained on a Hitachi 330 spectrophotometer. 

If a Fourier transform infrared spectrometer is being used, do not attempt to adjust the laser. Safety glasses must be worn in the laboratory at all times. Appropriate safety gloves and other personal protection equipment should be used when handling chemicals. 

IR spectra were obtained on a Model 10MX Nicolet Fourier Transform infrared spectrometer. IR films were spin-coated from polymer solutions in chlorobenzene on either KBr discs or silicon wafers polished on both sides. The samples were baked in vacuum at 90 C for at least 1 hour to ensure solvent removal. Film thicknesses were approximately 1 jtm, sufficient to remove interference fringe effects from the spectra. 

Fourier transform infrared spectrometers first appeared in the 1970s. These single beam instruments, which differ from scanning spectrometers, have an interferometer of the Michelson type placed between the source and the sample, replacing the monochromator (Figs 10.9c and 10.11). 

Figure 20-28 Layout of Fourier transform infrared spectrometer. [Courtesy Nlcolet. Madison. Wl.]...

Advantages of Fourier transform infrared spectrometers are so great that it is nearly impossible to purchase a dispersive infrared spectrometer. Fourier transform visible and ultraviolet spectrometers are not commercially available, because of the requirement to sample the interferometer at intervals of S = l/(2Av). For visible spectroscopy, Av could be 25 000 cm 1 (corresponding to 400 nm), giving S = 0.2 im and a mirror movement of 0.1 xm between data points. Such fine control over significant ranges of mirror motion is not feasible. 

For qualitative analysis, two detectors that can identify compounds are the mass spectrometer (Section 22-4) and the Fourier transform infrared spectrometer (Section 20-5). A peak can be identified by comparing its spectrum with a library of spectra recorded in a computer. For mass spectral identification, sometimes two prominent peaks are selected in the electron ionization spectrum. The quantitation ion is used for quantitative analysis. The confinnation ion is used for qualitative identification. For example, the confirmation ion might be expected to be 65% as abundant as the quantitation ion. If the observed abundance is not close to 65%, then we suspect that the compound is misidentified. 

Measurements either from the ground or from satellites have been a major contribution to this effort, and satellite instruments such as LIMS (Limb Infrared Monitor of the Stratosphere) on the Nimbus 7 satellite (I) in 1979 and ATMOS (Atmospheric Trace Molecular Spectroscopy instrument), a Fourier transform infrared spectrometer aboard Spacelab 3 (2) in 1987, have produced valuable data sets that still challenge our models. But these remote techniques are not always adequate for resolving photochemistry on the small scale, particularly in the lower stratosphere. In some cases, the altitude resolution provided by remote techniques has been insufficient to provide unambiguous concentrations of trace gas species at specific altitudes. Insufficient altitude resolution is a handicap particularly for those trace species with large gradients in either altitude or latitude. Often only the most abundant species can be measured. Many of the reactive trace gases, the key species in most chemical transformations, have small abundances that are difficult to detect accurately from remote platforms. 

Spectra of various aqueous solutions, including 1.8 M D-glucose solution were measured171 with a Fourier-transform, infrared spectrometer. The data obtained for dilute solutions were found useful for the usual qualitative purposes, and also amenable to quantitative analysis, but the spectra of such concentrated solutions as 1.8 M D-glucose show distortions of the background at >3000 cm-1, and negative, water deformation bands. These distortions were attributed to structural changes of water in the presence of the solutes. 

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