Fourier transform infrared spectroscopy presentation modes

There have been a number of important developments in light-based detection for CE since the previous edition of this work was published. For example, multichannel detection has become more common for absorbance as well as fluorescence, and Fourier transform infrared (FTIR) and nuclear magnetic resonance spectroscopies are now viable detection modes. Thus, while the purpose of this chapter is to describe the instrumentation and performance of more common optical detectors, newer methods are presented throughout. 

Identification of the specific species of the adsorbed oxyanion as well as mode of bonding to the oxide surface is often possible using a combination of Fourier Transform Infrared (FTIR) spectroscopy, electrophoretic mobility (EM) and sorption-proton balance data. This information is required for selection of realistic surface species when using surface complexation models and prediction of oxyanion transport. Earlier, limited IR research on surface speciation was conducted under dry conditions, thus results may not correspond to those for natural systems where surface species may be hydrated. In this study we review adsorbed phosphate, carbonate, borate, selenate, selenite, and molybdate species on aluminum and iron oxides using FTIR spectroscopy in both Attenuated Total Reflectance (ATR) and Diffuse Reflectance Infrared Fourier Transform (DRIFT) modes. We present new FTIR, EM, and titration information on adsorbed arsenate and arsenite. Using these techniques we... 

Many aspects of surface science and surface spec troscopy are concerned with the geometrical structure of surfaces, the composition of the surface and the identification of adatoms that may be present. Vibrational spectroscopy is a method for direct measurement of specific chemical bonds of adsorbed atoms and molecules, both between the adsorbate and the surface and the adatoms themselves. In the early days of HREELS, the 1970s, an added attraction for this type of spectroscopy was the ability to observe adsorbate surface bonding modes (often <125 meV = 1000 cm ), because the infrared spectrometers of the day used grating spectrometers, and IR detectors that were useful only above 1600 cm . The low cost and versatile Fourier transform infrared spectrometer (FTIR) and improved detector technology have eclipsed HREELS for routine surface chemical bond analysis. There are, however, some surface processes that can only be observed with electrons. Some diagnostic benefits that are related to the scattering mechanisms operative in HREELS continue to be useful for surface science. It should be noted that HREELS is usually performed on a known adsorbate, with a focus on the details of a specific adsorption system. HREELS is seldom used for the identification of unknown adsorbate species. 

The scope for IR spectroscopic techniques for direct in-polymer additive analysis is much broader than for extracts. In many real-life cases the form of the sample as presented for analysis is not at all suitable for routine transmission spectroscopy, which would, of course, have been the only method feasible with dispersive IR instruments. Most real-life samples are much too intensely absorbing or scattering for this to be possible. Yet, this does not preclude their routine measurement with Fourier transform spectrometers with the variety of sampling modes. In situ infrared analysis has been used for a host of analytical problems, as indicated in Table 1.10. 

The structurally related ri-form has received less study [58,59] but in both cases it has been concluded that three different types of surface Lewis site - strong, medium, and weak - are present. Our initial examinations (Figures 7.7 and 7.8) of activated tj-alumina, by observing desorption of a saturated chemisorbed py overlayer, through diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) observation of the py 8a mode band intensity at various temperatures, were in accord with this view [60]. The application of inelastic... 

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