Attenuated total reflectance infrared spectra

Attenuated total reflectance Infrared spectra were obtained on the oriented polystyrene sample (Figure 1) and on the two SMA copolymers selected for investigation (Figure 2,3). 

G. Janatsch, J.D. Kruse-Jarres, R. Marbach, H.M. Heise, Multivariate CaUbration for Assays in Clinical Chemistry using Attenuated Total Reflection Infrared Spectra of Human Blood Plasma , Anal. Chem., 61, 2016-2023 (1989). 

Boulet-Audet, M. et aL (2010) Quantitative determination of band distortions in diamond attenuated total reflectance infrared spectra. J. Phys. Chem. B, 114 (24), 8255-8261. 

Full attenuated total reflectance infrared spectrum of etodolac. 

Figure 8. Fingerprint region of the attenuated total reflectance infrared spectrum of etodolac.

Experiments were performed to determine if monomers containing 2-cyanoacrylates were grafted, that is bonded covalently, to bone. Bone slabs were primed with 1% solution of triethylamine in n-hexane, and an ethyl cyanoacrylate was spread on the treated bone. Two hours after application of the adhesive, the attenuated total reflectance infrared spectrum showed clearly the presence of... 

Figure 66. Typical attenuated total reflectance infrared spectrum of an invert emulsion oil-based drilling fluid. (Reproduced with permission from reference 182. Copyright 1994.)...

The infrared spectrum of amodiaquine has been determined in KBr disc (4). The principal peaks in the infrared spectrum of amodiaquine hydrochloride (KBr disc) are reported at 1565, 815, 1535, 1255, 869, 847 cm (7). Attenuated total reflectance infrared spectrum is used to detect amodiaquine hydrochloride in the solid state as a layer of crystals on adhesive tape. The method has been applied to the identification of the drug in tablet formulations. Common excipients such as starch, and... 

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... 

For opaque samples, such as fibers or paint chips, attenuated total reflectance-infrared (ATR-IR) spectroscopy is more commonly used. The sample is positioned over a crystal, and pressure is applied to ensure good contact between the sample and crystal. Infiared radiation is passed through the crystal, and because of the close contact, the radiation penetrates a small depth into the sample. Certain energies are absorbed depending on the chemical bonds within the sample, resulting in the characteristic spectrum of the sample. 

Figure 3 Typical beam path configuration for collecting an FTIR spectrum using an attenuated total reflectance element Iq is the incident infrared beam, f is the exiting beam.

A majority of traditional NIR measurements are made on solid materials and these involve reflectance measurements, notably via diffuse reflectance. Likewise, in the mid-IR not all spectral measurements involve the transmission of radiation. Such measurements include internal reflectance (also known as attenuated total reflectance, ATR), external reflectance (front surface, mirror -style or specular reflectance), bulk diffuse reflectance (less common in the mid-IR compared to NIR), and photoacoustic determinations. Photoacoustic detection has been applied to trace-level gas measurements and commercial instruments are available based on this mode of detection. It is important to note that the photoacoustic spectrum is a direct measurement of infrared absorption. While most infrared spectra are either directly or indirectly correlated... 

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. 

Many polymers are too tough to be ground even at liquid nitrogen temperatures. Consequently, surface techniques are often used. Internal reflectance or attenuated total reflectance (ATR) is the second most commonly used infrared technique [38-40]. For soft or pliable polymers or solutions, ATR is an extremely versatile technique and the spectrum is similar to a transmission spectrum. Unlike transmission, the spectrum obtained is independent of sample thickness. 

One other in situ technique can be used to determine fractional acidity in atmospheric aerosols by means of Fourier transform infrared (FTIR) spectroscopy (46). Originally, impactor samples were collected and were pressed into a KBr matrix, and then the IR spectrum was taken by attenuated total reflectance (ATR) FTIR spectroscopy to determine relative acidity, based on differences in absorption bands for sulfate and bisulfate species. Aerosols with [H+]/[S042 ] ratios greater than 1 could also be qualitatively identified. More recent innovations in the FTIR technique (47, 48) have made possible... 

Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy. Attenuated total reflectance (atr) ftir spectroscopy is based on the principle of total internal reflection (40). Methods based on internal reflection in the uv and visible regions of the spectrum are also common in addition to those in the ir region. The implementation of internal reflection in the ir region of the spectrum provides a means of obtaining ir spectra of surfaces or interfaces, thus providing molecularly-specific vibrational information. 

The most commonly used technique for obtaining a spectrum is the attenuated total reflectance (ATR) method in the multiple internal reflectance (MIR) mode. In this method, the infrared beam is passed into a special crystal of a selenide (KRS-5). The angle of incidence is such that the beam will bounce along the crystal. A sample of the polyurethane is placed hard up against the crystal. The infrared just penetrates into the material before it continues down the crystal. A number of internal bounces are obtained along the crystal. Up to 25 reflectances are obtained from a 2 mm crystal. Figure 9.8 illustrates the infrared path in an ATR cell. 

Sampling in surface-enhanced Raman and infrared spectroscopy is intimately linked to the optical enhancement induced by arrays and fractals of hot metal particles, primarily of silver and gold. The key to both techniques is preparation of the metal particles either in a suspension or as architectures on the surface of substrates. We will therefore detail the preparation and self-assembly methods used to obtain films, sols, and arrayed architectures coupled with the methods of adsorbing the species of interest on them to obtain optimal enhancement of the Raman and infrared signatures. Surface-enhanced Raman spectroscopy (SERS) has been more widely used and studied because of the relative ease of the sampling process and the ready availability of lasers in the visible range of the optical spectrum. Surface-enhanced infrared spectroscopy (SEIRA) using attenuated total reflection coupled to Fourier transform infrared spectroscopy, on the other hand, is an attractive alternative to SERS but has yet to be widely applied in analytical chemistry. 

This article shows how the evanescent wave can be used with advantage for spectroscopic purposes in the field of biomedical engineering. Three types of spectroscopy can be done with the evanescent wave in the UV-VIS range of the spectrum (a) attenuated total reflection (ATR) spectroscopy, which is well known in the infrared (b) the excitation of Raman scattering with the evanescent wave and (c) the excitation of fluorescence with the evanescent wave. The first two types will be discussed in this article the third is discussed for example by Hirschfeld U) and more recently by Watkins and Robertson (2). But before going into details a historical review may be of some interest. 

Infrared, like the UV and visible regions of the spectrum, provides a useful method for detecting solutes in liquid streams. The detector uses the principle of attenuated total reflectance, with a single beam spectrometer being used in conjunction with a tow volume flow cell. The cell is equipped with sodium chloride, calcium fluoride or zinc selenide windows and can be heated to temperatures greater than 100°C. The detector can... 

The infrared absorption spectrum of sulfacetamide sodium has been determined in KBr disc (4). The principal peaks appear at 825, 1090,1145,1264,1552,1600 cm 1. The infrared stretching frequencies of the amino group have been used to calculate the force constant, the band angle and the "S" character of the nitrogen orbitals of the N-H band (23,24). Infrared measurements of sulfonamides have been performed to study the imide-amide tautomerism (25) and to see if there is any change in the electronegativity of the SO2 group (26,27). Sulfacetamide in eye-drops and ointments has been identified by attenuated total reflectance (ATR) infrared spectra (28). 

Internal reflection spectroscopy (2), also known as attenuated total reflectance (ATR), is a versatile, nondestructive technique for obtaining the IR spectrum of the surface of a material or the spectrum of materials either too thick or too strongly absorbing to be analyzed by standard transmission spectroscopy. The technique goes back to Newton who, in studies of the total reflection light at the interface between two media of different retractive indices, discovered that an evanescent wave in the less dense medium extends beyond the reflecting interface. Infrared spectra can conveniently be obtained by measuring the interaction of the evanescent wave with the external less dense medium. 

A method of horizontal attenuated total reflectance (HATR) by Fourier transform infrared spectroscopy (FTIR) is considered more useful for infrared spectroscopic analysis of leather samples. By this method, the sample is simply put on the flat plate of ZnSe crystal or KRS-5 crystal of the HATR accessory. The Fourier transformation of the interferogram is converted by the computer into a plot of absorption against wave number that resembles the usual IR spectrum (William and Fleming, 1998). 

The internal reflectance technique is usually called attenuated total reflection (ATR) spectroscopy. It is especially useful for studying strongly absorbing media, for example, aqueous solutions. When the infrared radiation is absorbed in the test medium, one obtains a spectrum similar to that from a transmission experiment. However, there are distortions in the ATR spectrum, especially in the region of intense bands. One reason for distortion is the fact that the depth of penetration varies with wavelength. The other effect is due to the change of the refractive index of the solution in the region of the intense band. ATR spectra should be corrected for these effects so that they may be compared to normal transmission spectra. 

Infrared spectra can also be obtained by reflecting the IR beam on the surface of a sample. This technique is applied when it is not possible to obtain an IR spectrum by a transmission technique. Attenuated total reflectance (ATR) also known as ATIR (attenuated total internal reflectance) is based on multiple internal reflectance of the IR beam on the sample surface using a high refractive index crystal (e.g.. 

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