Internal-reflection element

The real utility of d comes in the analysis of thin films. Consider a substrate of refractive index supporting a thin film of thickness d and refractive index in contact with an internal reflection element (the prism) of refractive index as shown in Figure 24. In this case, d depends on the polarization of the incident light beam and is given by... 

Atr—ftir can be readily performed on most commercial ftir spectrometers through the use of an attachment for atr spectroscopy. These devices provide ir-transparent internal reflection elements that are typically made of Ge, KRS-5, ZnSe, or ZnS. These internal reflection elements are made of materials that are of extremely high purity to avoid losses from absorption by impurities in these devices. Coupling of a thin film or surface sample to one of these reflection elements is accompHshed by pressing the sample against the element while acquiring the spectmm. 

Thin-fdm was prepared from a slurry of catalyst powder which was prepared from 10 mg catalyst in 5 ml of 2-propanol. The catalyst slurry was sonicated for 30 min. and allowed to sit stagnant overnight. Before preparing the films, the slurry was sonicated for 15 min., 20 drops (0.1 ml) were added onto a ZnSe trough plate internal reflection element (022-2010-45, Pike Technologies). The solvent was allowed to evaporate, the procedure was repeated a total of five times. After drying in air at room temperature, the catalyst thin-film was ready for 2-propanol dehydrogenation studies. 

Always based on the use of IR spectrophotometry, a novel attenuated total reflection-Fourier-transform infrared (ATR-FTIR) sensor [42] was proposed for the on-line monitoring of a dechlorination process. Organohalogenated compounds such as trichloroethylene (TCE), tetrachloroethylene (PCE) and carbon tetrachloride (CT) were detected with a limit of a few milligrams per litre, after extraction on the ATR internal-reflection element coated with a hydro-phobic polymer. As for all IR techniques, partial least squares (PLS) calibration models are needed. As previously, this system is promising for bioprocess control and optimization. 

In this method, the sample (such as a polymer film) is pressed against a transparent material having a high refractive index (called the internal reflection element (IRE)). The IR light beam passes through this material, rather than air, before and after reflecting from the sample, hence the reason for describing... 

Table 6.3 Common IR transmitting materials used for IR optics and ATR Internal reflectance elements (IREs)...

ESR electron spin resonance IRE internal reflectance element... 

Fig. 24. Attenuated total reflectance of thin film of thickness d and refractive index n2 on a substrate of refractive index 3 at the surface of internal reflection element (IRE) of refractive index nv Decay of evanescent field beyond thickness of thin film indicated.

Attenuated total reflection FTIR is a well-established technique for obtaining absorbance spectra of opaque samples. The mode of interaction is unique because the probing radiation is propagated in a high index-of-refraction internal reflection element (IRE). The radiation interacts with the material of interest, which is in close contact with the IRE, forming an interface across which a nonpropagating evanescent field penetrates the surface of the material of interest to a depth in the order of one wavelength of the radiation. The electric field at the interface penetrates the rarer medium in the form of an evanescent field whose amplitude decays exponentially with distance into the rarer medium. 

Protein Adsorption. The development of medical implant polymers has stimulated interest in the use of ATR techniques for monitoring the kinetics of adsorption of proteins involved in thrombogenesis onto polymer surfaces. Such studies employ optical accessories in which an aqueous protein solution (93) or even ex - vivo whole blood (94-%) can be flowed over the surface of the internal reflection element (IRE), which may be coated with a thin layer of the experimental polymer. Modem FT-IR spectrometers are rapid - scanning devices, and hence spectra of the protein layer adsorbed onto the IRE can be computed from a series of inteiferograms recorded continuously in time, yielding ah effective time resolution of as little as 0.8 s early in the kinetic runs. Such capability is important because of the rapid changes in the composition of the adsorbed protein layers which can occur in the first several minutes (97). 

The adsorption of albumin from aqueous solution onto copper and nickel films and the adsorption of B-lactoglobulin, gum arabic, and alginic acid onto germanium were studied. Thin metallic films (3-4 nm) were deposited onto germanium internal reflection elements by physical vapor deposition. Transmission electron microscopy studies indicated that the deposits were full density. Substrate temperature strongly Influenced the surface structure of the metal deposits. Protein and/or polysaccharide were adsorbed onto the solid substrates from flowing... 

Attenuated total refectance (ATR) infrared spectroscopy has been used to identify chemical species that are adsorbed to a germanium internal reflection element (IRE). We have described a method for depositing thin... 

In an effort to gain a better understanding of the initial fouling step leading to bacterial attachment and biofilm formation, we have investigated the adsorption of protein and polysaccharides onto thin metallic films and uncoated internal reflection elements from flowing solutions using attenuated total reflectance spectroscopy. The preliminary results will be described in this paper. 

An alternative to supporting the mica on an internal reflection element is to use thicker mica sheets as windows in a liquid transmission cell. The thicker mica was required to prevent the deformation or tearing of the mica when liquids were injected into the cell, but this returned us to the... 

Time - resolved spectra of a solid hydrocarbon layer on the surface of an internal reflection element, interacting with an aqueous solution of a nonionic surfactant, can be used to monitor the detergency process. Changes in the intensity and frequency of the CH2 stretching bands, and the appearance of defect bands due to gauche conformers indicate penetration of surfactant into the hydrocaibon layer. Perturbation of the hydrocarbon crystal structure, followed by displacement of solid hydrocaibon from the IRE surface, are important aspects of solid soil removal. Surfactant bath temperature influences detergency through its effects on both the phase behavior of the surfactant solution and its penetration rate into the hydrocaibon layer. 

Attenuated total reflection infrared (IR) spectra are obtained by pressing the sample against an internal reflection element (IRE) [e.g., zinc selenide (ZnSe) or germanium (Ge)]. IR radiation is focused onto the end of the IRE. 

Figure 10.4. Total internal reflection at the interface of an internal reflection element (IRE). Depth of penetration of the evanescent wave is approximately 1 pm. The top picture depicts the evanescent beam in more detail. The sample is coated on both sides of the IRE.

Samples for SEIRA are typically in the form of molecular monolayers deposited on both sides of the internal reflection element or ATR plate, which is usually a silicon crystal. The silicon substrate is cut in the paral-... 

Biirgi (2005) described equipment combining attenuated total reflection IR with reflectance UV-vis spectroscopy. A fiber optical probe was positioned parallel to the surface normal of the internal reflection element in front of a fused silica window in the reactor. The distance from the probe to the catalyst layer was about 4 mm. A second fiber optical arrangement allowed simultaneous acquisition of transmission UV-vis spectra of the effluent liquid from the reactor cell. All measurements were performed with the catalyst at 303 K. 

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