Internal reflection infrared spectroscop

These investigations were aided substantially by use of the multiple attenuated internal reflection (MAIR) spectroscopic technique to record surface specific, infrared (IR) spectra in order to determine structure and monitor preparation and cleaning methods. 

In view of the discussed above discrepancies, some spectroscopic evidence of particular surface species used in the MUSIC model would be much desired. Connor et al. [51] studied internal reflection infrared spectra of Ti02 (amorphous + anatase) films, and obtained the following speciation. The (=Ti)20H species is formed at pH < 4.3, and =TiOH2 at pH < 5. The =TiOH species was detected at pH 4.3-10.7 (maximum abundance at pH 8) and =TiOH2 species at pH < 10.7. 

Final justification for using terms such as inner- or outer-sphere awaits direct spectroscopic confirmation. Electron Spin Resonance, Mossbauer, and Fourier Transform Infrared-Cylindrical Internal Reflection Spectroscopic techniques are being used to establish the structure of surface complexes (see, e.g., McBride, Ambe et al., and Zeltner et al., this volume). The potential for using EXAFS (extended x-ray absorption fine structure) to establish the type of surface complex for Pb + adsorbing onto goethite is currently being undertaken in our laboratory. 

To put things into perspective, we. can broadly classify these analytical methods into bulk, dry surface, and in situ interfacial techniques. This chapter focuses on the last category, illustrating two in situ techniques used to study anion binding at the goethite (a-FeOOH)-water interface titration calorimetry and cylindrical internal reflection-Fourier transform infrared (CIR-FTIR) spectroscopy. In fact, CIR-FTIR could prove to be extremely powerful, since it allows direct spectroscopic observation of ions adsorbed at the mineral-water interface. 

Holmen, B.A. Tejedor-Tejedor, M.S. Casey, WA. (1997) Hydroxymate complexes in solution at the goethite/water interface. A. Cylindrical internal reflectance Fourier transform infrared spectroscopic study. Langmuir 13 2197... 

The increasing application of spectroscopic methods in electrochemistry has characterized the last decade and marked the beginning of new developments in electrochemical science [1]. Among these methods, in-situ infrared spectroscopy provides a very useful tool for characterizing the electrode-solution interface at a molecular level. First in-situ infrared (IR) electrochemical measurements were performed in 1966 [2] using the internal reflection form [3]. However, problems in obtaining very thin metal layers on the surface of the prisms used as IR windows, delayed the extensive application of in-situ IR spectroscopy until 1980, when the method was applied in the external reflection form [4]. The importance of this step does not need to be emphasized today. 

Let us call this the donor-acceptor complex proposal, similar to that presented recently for adsorption of substituted nitrobenzenes and nitrophenols on mineral surfaces [739]. The experiments on which this proposal is based are (1) isotherms of phenol, nitrobenzene, and m- and / -nitrophenol on one commercial activated carbon at pH = 2-7 and very low solute concentrations ( <1.5% of the solubility limit of these species [6]) and (2) detailed infrared (internal reflection) spectroscopic analysis of the surface after adsorption of / -nitrophenol. Interestingly, neither in this study, nor in any subsequent study that supports this mechanism, has a similar analysis been performed with carbons containing varying concentrations of carbonyl surface groups. Also of interest is that the authors dismiss the electrostatic explanation of the reported pH effects by assuming that the isoelectric point of the carbon (which was dried at 200°C for 12-24 h) was ca. 2.4. 

The use of infrared spectroscopy in the Earth and environmental sciences has been widespread for decades however, until development of the attenuated total reflectance (ATR) technique, the primary use was ex situ material characterization (Chen and Gardella, 1998 Tejedor-Tejedor et al., 1998 Degenhardt and McQuillan, 1999 Peak et al., 1999 Wijnja and Schulthess, 1999 Aral and Sparks, 2001 Kirwan et al., 2003). For the study of environmental systems, the strength of the ATR-Fourier transform infrared (FTIR) technique lies in its intrinsic surface sensitivity. Spectra are collected only from absorptions of an evanescent wave with a maximum penetration depth of several micrometers from the internal reflection element into the solution phase (Harrick, 1967). This short optical path length allows one to overcome any absorption due to an aqueous phase associated with the sample while maintaining a high sensitivity to species at the mineral-water interface (McQuillan, 2001). Therefore, ATR—FTIR represents a technique capable of performing in situ spectroscopic studies in real time. 

Surface characterization by spectroscopic techniques yields information on the functional groups and elemental composition on the surface of polymeric biomaterials. The most common spectroscopic tools used for biomedical polymers are X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), secondary ion mass spectrometry (SIMS), and Fourier transform infrared spectroscopy (FTIR) (diffuse reflectance and attenuated total internal reflectance modes). Each of these techniques is discussed in the succeeding text. 

Adsorption dynamics Ruorescence spectroscopy and microscopy (including immunofluorescence, total internal reflection fluorescence) Attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) Quartz crystal microbalance (Spectroscopic) eUipsometry Reflectometric interference spectroscopy... 

When light traversing an optically dense medium approaches an interface with a more optically rare medium at an angle exceeding a critical value, Bent = sin (rerare/ dens), total internal reflection occurs and an evanescent wave of exponentially deca5ung intensity penetrates the rarer medium. This phenomenon is at the heart of certain spectroscopic methods used to probe biomolecules at interfaces (199). In total internal reflection fluorescence (TIRF) spectroscopy (200-202), the evanescent wave excites fluorescent probes attached to the biomolecules, and detection of the emission associated with their decay provides information on the density, composition, and conformation of adsorbed molecules. In fourier transform infrared attenuated total reflection (FTIR-ATIR) spectroscopy (203,204), the evanescent wave excites certain molecular vibrational degrees of freedom, and the detected loss in intensity due to these absorbances can provide quantitative data on density, composition, and conformation. 

In the reflection mode, typically specular reflectance is measured on the electrode surface. It is anticipated that the variation of the surface structure (e.g., surface adsorption, phase transitions, etc.) will result in appreciable changes in the reflectivity properties. One can thus correlate the structural characterislics gleaned from spectroscopic measurements with electrochanical results. Figure 2.15 shows a cell assembly for internal reflection spectroelectrochemistry. Several spectroscopic techniques have been used, such as infrared, surface plasmon resonance, and X-ray based techniques (reflectivity, standing wave, etc.). Figure 2.16 depicts a cell setup for (A) infrared spectroelectrochemistry (IR-SEC) and (B) surface X-ray diffraction. 

These workers developed dynamic compression modulation attenuated total reflection Fourier transform infrared spectroscopic methods for characterising polymer films. To obtain dynamic compression polarised ATR spectra, internal reflection element (IRE) secure assemblies made of tungsten carbide with very high hardness were designed. 

For most transmission spectroscopic measurements made with a microscope, the sample is in contact with air and so n is usually approximately equal to 1. Since for most microscopes 9 40°, NA is usually close to 0.6 (sin 40° = 0.64). Thus, the spatial resolution is approximately equal to 2. (We note here that the Abbe resolution is often defined as 2/2, but this performance is only accomplished for coherent illumination.) For mid-infrared measurements at the highest spatial resolution, it is customary to set the microscope aperture to give the diffraction-limited resolution at 1000 cm (2 = 10 pm) so that the resolution at longer wavelengths is set by the value at 1000 cm (about 10 pm). Better resolution is achieved in attenuated total reflection (ATR), especially when the internal reflection element (IRE) is silicon (n = 3.4) or germanium (n = 4.0), but achieving optical spatial resolution better than about 3 pm is essentially impossible for diffraction-limited mid-infrared measurements. 

Spectroscopic Methods UV-VIS Spectroscopy Fourier Transform Infrared FITR Internal Reflection ATR External Reflection RA Emission Spectroscopy Difiuse Reflectance DRIFT Infrared Microscopy Photoacoustic Spectroscopy PA Rheo-Photoacoustic Spect. RPA Ellipsometiy... 

A novel combination of SECM with mid-infrared (IR) (3-25 pm wavelength region) spectroscopy was reported by Kranz et al. [158,159]. Here, the SECM substrate is the flat top of a hemispherical ZnSe attenuated total reflection (ATR) single bounce crystal. IR radiation is directed through the crystal and focused onto a small spot at the ATR crystal-solution interface. The locally created evanescent field penetrates a few microns into solution and the radiation reflected at the interface (internally reflected) is directed toward a photodetector. Hence, IR-adsorbing molecules present in the close vicinity of the interface can be spectroscopically probed, that is, an evanescent field adsorption spectrnm is acquired. 

This unit describes the attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopic method (AOCS, 1999a AOAC International, 2000), a novel method for measuring the total amount of fat with isolated trans double bonds. It is applicable to natural fats (ruminant fats) and processed fats and oils (partially hydrogenated fats and oils or refined vegetable oils) consisting of long-chain fatty acid methyl esters or triacylglycerols with trans levels >5%, as percent of total fat (AOAC International, 2000). 

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