FT-IR reflection-absorption spectroscopy

Other recent applications of FT-IR in pharmaceutical analysis include reaction monitoring by fiberoptic FT-IR/ATR spectroscopy140 and stability studies of pharmaceutical emulsions using FT-IR microscopy.141 A novel equipment cleaning verification procedure using grazing angle fiberoptic FT-IR reflection-absorption spectroscopy was described by Perston et al.142... 

For molecular properties of the TAG polymorphs, local molecular structural information such as methyl-end group, olefinic conformation, and chain-chain interaction are unveiled by infrared (IR) spectroscopy, especially Fourier-transformed infrared spectroscopy (FT-IR) (23, 24). Compared with a pioneering work by Chapman (25), great progress has been achieved by using various FT-IR techniques, such as polarized transmission FT-IR, reflection absorption spectroscopy (RAS), and attenuated total reflection (ATR) (26-28). 

FT-IRRAS FT-IR reflection-absorption spectroscopy ISE ion selective electrode... 

Recent work in our laboratory has shown that Fourier Transform Infrared Reflection Absorption Spectroscopy (FT-IRRAS) can be used routinely to measure vibrational spectra of a monolayer on a low area metal surface. To achieve sensitivity and resolution, a pseudo-double beam, polarization modulation technique was integrated into the FT-IR experiment. We have shown applicability of FT-IRRAS to spectral measurements of surface adsorbates in the presence of a surrounding infrared absorbing gas or liquid as well as measurements in the UHV. We now show progress toward situ measurement of thermal and hydration induced conformational changes of adsorbate structure. The design of the cell and some preliminary measurements will be discussed. 

Synthetic surfactants and polymers are probably most often used to modify the characteristics of a solid surface, i.e., they function at the solid - liquid interface, such as in the processes of detergency, lubrication, or the formation of adhesive bonds. The performance of modem FT - IR spectrometers is such that many new applications to the characterization of the solid - liquid interface, particularly in kinetics studies, are possible. Reflection - absorption spectroscopy and attenuated total reflectance (ATR) techniques have been applied to "wet" interfaces, even the air - water interface, and have figured prominently in recent studies of "self -assembled" mono - and multilayers. 

The technique using p-s modulation has received different names depending on the kind of IR instrument used. Thus for grating instruments it was called PMIRRAS (polarization modulation infrared reflection-absorption spectroscopy) [6]. For FT spectrometers the name FTIRRAS [8] was suggested. However this name was later used also in connection with Fourier transform spectra applying the potential difference approach. 

Films are also characterized [129,132] with FT-IR spectroscopy and it is customary to use transmission and infrared reflection absorption spectroscopy (IR-RAS) to study the orientation. The films are prepared on a modified Lauda film balance and the thickness as well as conductivity depends on the mole ratio of monomers in the dispersing solvent. Varying this ratio results in the formation of films at the air-water interface ranging in thickness from 1 monolayer to multilayers. The most highly conducting films are produced with mole ratios of pyrrole to 3-octadecyl-pyrrole of 5,000 1. 

Mirabella and Koberstein have previously shown the benefit of DSC/FT-IR for polymer characterization (3,4). In this work, the same epoxy system described above in the uncured state was analyzed by DSC/FT-IR. Thin films of uncured amine-activated epoxies were placed in the sample pan of the FP84 and heated from 25 to 280 °C at 10 C per minute. Changes in the structure of the epoxy as a fimction of temperature were recorded simultaneously by infrared spectroscopy. The sample was relatively transmissive to infirared radiation. The beam transmitted down through the sample, reflected off the aluminum cup, and passed back up through the material. This type of analysis is called reflection/absorption spectroscopy. A "well behaved" absorbance spectrum was generated directly without any need for correction. To produce a sufficient signal on the DSC, the bulk of the sample had to be placed on the reference side. 

Changes in wheat carbohydrate chemistry due to chemical enzymatic degradation were measured on a macro scale by internal reflection (attenuated total reflection ATR) FT-IR spectroscopy from a spot size of 250 X 250 gm [51]. In this study, the absorption bands of sucrose, fructose, glucose, arabinose and galactose were identified, and spectra included for mahogany, huckleberry and oak, as well as for cellulose and cellophane. Both, principal component analysis (PCA) and plotting of PCI versus PC2 enabled distinctions to be made between filter paper, cello-... 

Characterization of catalysts The zeolite structure was checked by X-ray diffraction patterns recorded on a CGR Theta 60 instrument using Cu Ka, filtered radiation. The chemical composition of the catalysts was determined by atomic absorption analysis after dissolution of the sample (SCA-CNRS, Solaize, France). Micropore volumes were measured by N2 adsorption at 77 K using a Micromeritics ASAP 2000 apparatus and by adsorption of cyclohexane (at P/Po=0.15) using a microbalance apparatus SET ARAM SF 85. Incorporation of tetrahedral cobalt (II) in the framework of Co-Al-BEA and Co-B-BEA was confirmed by electronic spectroscopy [18] using a Perkin Elmer Lambda 14 UV-visible diffuse reflectance spectrophotometer. Acidity measurements were performed by Fourier transform infrared spectroscopy (FT-IR, Nicolet FTIR 320) after pyridine adsorption. Self-supported wafer of pure zeolite (20 mg/cm ) was outgassed at 673 K for 6 hours at a pressure of lO Pa. After cooling at 423 K, the zeolite was saturated with pyridine vapour (30 kPa) for 5 min, evacuated at this temperature for 30 min and the IR spectrum was recorded. 

The Pr(II) and Nd(III) complexes of three pentoses, three hexoses and two disaccharides were characterized by various spectral and analytical techniques including FT IR, C NMR, solution absorption and solid-state diffused reflectance spectroscopy, magnetic susceptibility and CD measurements, as well as cyclic voltammetry and thermal analysis. ... 

Gobernado-Mitre et alP studied the molecular organization of CuNc onto different substrates using IR and SERS a tilted, close to face-on molecular orientation in the evaporated films on KBr and Ag was inferred from the transmission and reflection-absorption FT-IR spectroscopy. 

Characterize the surface of the fiber component or a metallic inclusion Sellitti et al. (1988) used FT-IR attenuated total reflection spectroscopy to characterize the surface of graphitized carbon fibers and identify the functional groups, and reactions between the fibers and an epoxy resin coating were investigated. Devaty (1989) evaluated the IR absorption of composites with metalUc particles. 

The methods of presenting samples such as a tissue or isolated single cell for study in an FT-IR microscope have to date been predominantly confined to transmission and, the so-called, transflection sampling techniques. The latter is actually a reflection-absorption technique vide infra). Of increasing recent interest is use of the so-called ATR sampling technique for the analysis of tissue samples. ATR is an abbreviation for attenuated total reflection and is an internal reflection spectroscopy technique. On the horizon are perhaps nearfield techniques. Each of these will now be considered in turn. 

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