Attenuated total reflection spectroscopy ATR

Fluctuations in the dielectric properties near the interface lead to scattering of the EW as well as changes in the intensity of the internally reflected wave. Changes in optical absorption can be detected in the internally reflected beam and lead to the well-known technique of attenuated total reflectance spectroscopy (ATR). Changes in the real part of the dielectric function lead to scattering, which is the main topic of this review. Polarization of the incident beam is important. For s polarization (electric field vector perpendicular to the plane defined by the incident and reflected beams or parallel to the interface), there is no electric held component normal to the interface, and the electric field is continuous across the interface. For p polarization (electric field vector parallel to the plane defined by the incident and reflected beams), there is a finite electric field component normal to the interface. In macroscopic electrodynamics this normal component is discontinuous across the interface, and the discontinuity is related to the induced surface charge at the interface. Such discontinuity is unphysical on the molecular scale [4], and the macroscopic formalism may have to be re-examined if it is applied to molecules within a few A of the interface. 

The polymer properties in thin films are then compared with the bulk as measured by FTIR attenuated total reflection spectroscopy (ATR). A modest refractive index of the internal reflection element (IRE made of ZnSe, n=2.43 at 2000 cm ) and an incident angle of 65° - still low but well above the critical angle of total reflection - are chosen for the p-polarized light in order to obtain an information depth of several microns. Hence, the ATR spectra provide the bulk properties of the polymer sample. 

Another variant of IR spectroscopic technique is known as Fourier Transform IR Attenuated Total Reflection Spectroscopy (ATR FT-IR) has been described by Poston et al. [123] to study adsorbates at the silica-solution interface. The authors reported the preparation of ZnSe internal-reflection elements coated with a porous silica layer of ca. 700 nm thick. They studied the adsorption of ethylacetate from n-heptane solutions. This technique allows the determination of IR spectra in-situ and its dependence on the solution concentration. They found a nonlinear adsorption isotherm of ethylacetate on... 

Spectra of insoluble solid phenolic prepolymers or crosslinked products can be recorded by diffuse reflectance (DRIFT) and attenual total reflection spectroscopy (ATR). Reflection spectroscopy techniques are qualitative methods for analysis of insoluble materials [228], which work by reflecting the infrared light off the surface of the material to be analyzed. Table 7 gives a summary of wavenumbers of absorbance bands in modified phenolic materials. 

Figure 3.10 FTIR spectra using attenuated total reflectance spectroscopy (ATR) in the range 4000-700 cm" of EVA copolymer degraded to various coloured states from colourless (virgin), yellow to brown through to black. Reproduced with permission from N.S. Allen, M. Edge, M. Rodriguez, C.M. Liauw and E. Fontan, Polymer Degradation and Stability, 2000,68, 3, 363. 2000, Elsevier [29]...

Attenuated Total Reflectance Spectroscopy (ATR). ATR, also called internal reflection spectroscopy, is a technique used to characterize the surface region of a polymeric composition. A sample is placed on both sides of an appropriate crystal and an infrared beam within the crystal is repeatedly attenuated as it is reflected back and forth from one sample surface to the other. The intensity of the attenuated... 

While electron or ion beam techniques can only be applied under ultra-high vacuum, optical techniques have no specific requirements concerning sample environment and are generally easier to use. The surface information which can be obtained is, however, quite different and mostly does not contain direct chemical information. While with infra-red attenuated total reflection spectroscopy (IR-ATR) a deep surface area with a typical depth of some micrometers is investigated, other techniques like phase-measurement interference microscopy (PMIM) have, due to interference effects, a much better surface sensitivity. PMIM is a very quick technique for surface roughness and homogeneity inspection with subnanometer resolution. 

In infra-red attenuated total reflection spectroscopy (IR-ATR) and grazing incidence reflection IR spectroscopy (IR-GIR) the evanescent wave of a totally... 

Adsorption phenomena from solutions onto sohd surfaces have been one of the important subjects in colloid and surface chemistry. Sophisticated application of adsorption has been demonstrated recently in the formation of self-assembhng monolayers and multilayers on various substrates [4,7], However, only a limited number of researchers have been devoted to the study of adsorption in binary hquid systems. The adsorption isotherm and colloidal stabihty measmement have been the main tools for these studies. The molecular level of characterization is needed to elucidate the phenomenon. We have employed the combination of smface forces measmement and Fomier transform infrared spectroscopy in attenuated total reflection (FTIR-ATR) to study the preferential (selective) adsorption of alcohol (methanol, ethanol, and propanol) onto glass surfaces from their binary mixtures with cyclohexane. Om studies have demonstrated the cluster formation of alcohol adsorbed on the surfaces and the long-range attraction associated with such adsorption. We may call these clusters macroclusters, because the thickness of the adsorbed alcohol layer is about 15 mn, which is quite large compared to the size of the alcohol. The following describes the results for the ethanol-cycohexane mixtures [10],... 

An infrared spectrum is a plot of percent radiation absorbed versus the frequency of the incident radiation given in wavenumbers (cm ) or in wave length ( xm). A variation of this method, diffuse reflectance spectroscopy, is used for samples with poor transmittance, e.g. cubic hematite crystals. Increased resolution and sensitivity as well as more rapid collection of data is provided by Fourier-transform-IR (FTIR), which averages a large number of spectra. Another IR technique makes use of attenuated total reflectance FTIR (ATR-FTIR) often using a cylindrical internal reflectance cell (CIR) (e.g. Tejedor-Tejedor Anderson, 1986). ATR enables wet systems and adsorbing species to be studied in situ. 

More recently, Markovich et al. (91) utilized a combination of solid-state infra-red (IR) and NMR methods to study the amorphous to crystalline API transition of SCH 48461 in solid dispersion capsule formulations. In this illustrative study, dissolution testing initially revealed inter-and intralot variations of capsules stored under accelerated stability conditions (25°C/60% RH, 30°C/60% RH, and 40°C/80% RH). PXRD analysis could not explain the dissolution data being collected on lots stored at accelerated conditions and revealed no differences from original diffraction patterns. Two additional analytical techniques, attenuated total reflectance IR (ATR-IR) spectroscopy and solid-state 13C NMR spectroscopy, were employed to study the physical form in the actual solid dispersion formulations. 

ID IQ 2D 2D-NMR 2h2o 2Q 3Q 9BEN A1 ABS AC ACM ACN AFM Al-CSM ALMA-i5 Al-m-EPDM AN AO APT ASTM ATR ATR-IR B/S BABA Two-dimensional Single-quantum One-dimensional Deuteron solid-state NMR Deuterated water Double-quantum Triple-quantum 9 borobicyclo [3, 3, 1] nonane Amide 1 Acrylonitrile-butadiene-styrene terpolymer Accelerator Acrylate rubber Acrylonitrile Atomic Force Microscopy Aluminium salt of chlorosulfonate polyethylene Allyl-rf5 methacrylate Aluminium salt of maleated EPDM Acrylonitrile 1-Allyl oxyoctane Attached Proton Test American Standards for Testing and Materials Attenuated total reflectance spectroscopy Attenuated total reflectance-IR spectroscopy Butadiene/styrene Back-to-back... 

It has been suggested that the first step of reaction (6) may be the formation of a carboxylic species COOHads. Carboxyl radicals have indeed been observed by Zhu et al." for potentials lower than 0.65 V using Fourier Transform infrared Reflectance Absorption Spectroscopy with the Attenuated Total Reflection mode (ATR-FTtR). Moreover Anderson et al." made numerical simulation which indicated that the formation of an adsorbed carboxylic species was energetically more favorable. Here, it has to be noted that the electro-oxidation of CO being a stracture sensitive reaction (sensitive to the superficial stracture symmehy" and to the presence of surface defects) this species can be used to study the activity of a catalyst but also as a molecular probe to characterize the catalytic surface. ... 

The only piece of experimental evidence for the orientation of apoA-I helices on DMPC discoidal complexes has come from the use of polarized attenuated total reflection infrared (ATR-IR) spectroscopy (Brasseur et al. (1990 Wald et al., 1990). Although internal reflection spectroscopy is not new (Harrick, 1967), its combination with polarized IR measurements of oriented biological membranes is a more recent application, which allows the spectrum to be taken in the presence of water. The technique has been used most frequently to study the orientation of lipid functional groups relative to the membrane plane in pure lipid bilayers (Fringeli and Gunthard, 1981 Holmgre et al., 1987 Okamura et al., 1990 Hubner and Mantsch, 1991), but has also been applied to studies of... 

ATR (Attenuated Total Reflection) spectroscopy [27] was invented and applied mainly for investigations of surfaces.This method entails an experimental set-up which reflects the IR beam via a mirror system to a crystal with a high refraction index. Normally, germanium (refraction index n = 4), silver chloride (n = 2) or diamond (n = 2,4) crystals are used. The crystal is standing in direct contact with the surface of the sample (Fig. 16.3). 

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