Attenuated total internal reflectance

Examples of nir analysis are polymer identification (126,127), pharmaceutical manufacturing (128), gasoline analysis (129,130), and on-line refinery process chemistry (131). Nir fiber optics have been used as immersion probes for monitoring pollutants in drainage waters by attenuated total internal reflectance (132). The usefulness of nir for aqueous systems has led to important biological and medical appHcations (133). 

Surface hydrogen is conveniently detected by MIR at attenuated-total-internal-reflection prisms of GaAs electrodes. Si-doped (100)-oriented n-GaAs single crystals were employed in the electrochemical cell illustrated schematically in Figure 3.3. 

Infrared spectra of zeolitic samples can be measured in several different modes. These include transmission, diffuse reflectance, attenuated total internal reflection (ATR) and emission. Transmission and diffuse reflectance are by far the most widely used of these techniques. In the transmission mode, the sample is placed directly in the infrared beam of the instrument and the light passing through or transmitted is measured by the detector. This transmitted signal (T) is ratioed to the open beam (no sample) signal (To) to get the transmission spectrum of the sample. The transmission spectrum is converted to an absorbance spectrum ... 

Short path length flow cells may be used in lower volume, or lower flow situations. The extremely small gap between the optics of fibers limits them to these types of applications. It is possible to make flow cells with sample gaps as small as 25 um, so that they may be used with highly absorbing species. With even higher absorbing species, attenuated total internal reflection (ATR) probes may be appropriate (see below). 

Figure 4.2 Schematic of basic probe designs transmission cell, immersion probe (retroreflecting and transmission), attenuated total internal reflection.

Attenuated total internal reflection (ATR) probes offer several advantages over other probe types. ATR is a phenomenon that relies on a difference in the index of refraction of a crystal and that of the solution with which it is in contact to prevent light from escaping the crystal. Only the evanescent wave of the light interacts with the solution layer at the crystal face. The result is an optical pathlength of only a few microns. Typical designs make use of faceted crystals or hemispheres (see Figure 6.1). The most common ATR material in the UV-vis is sapphire. In rare cases, fused silica may be used. ATR allows spectra to be taken of neat samples with optical density (OD) of 500-1000... 

Sommer, A. J., Tsinger, L. G., Marcott, C. and Story, G. M. (2001) Attenuated total internal reflection infrared mapping microspectroscopy using an imaging microscope. Appl. 

The absorption is very intense, so direct measurement of absorption spectra requires very thin films. When the sample surface is smooth enough, the absorption can be calculated by Kramers-Kronig inversion of the reflectance, which can be done rather accurately for a well-isolated transition [113]. A strongly scattering sample must be studied by attenuated total internal reflectance. 

Surface Analysis Attenuated Total Internal Reflectance (ATIR), EDX, Rutherford Backscattering (RBS), Electron Spectroscopy for Chemical Analysis (ESCA) also known as X-ray Photoelectron Spectroscopy (XPS), Secondary Ion Mass Spectrometry (SIMS), Ion Scattering Spectroscopy (ISS)... 

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.. 

Because infrared spectroscopy is an optical technique, the sample must be transparent in the spectral region of interest. Infrared spectroscopy can be used for heterogeneous samples and adsorbates on catalyst surfaces [11, 17]. If the sample cannot be made thin enough to be transparent, special probing techniques such as attenuated total internal reflectance can be use to monitor the concentration. 

Af-acetyl-i-tyrosine ethyl ester adsorption thin layer chromatography standard atmosphere adenosine triphosphate attenuated total internal reflection atomic weight... 

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. 

Attenuated Total Internal Reflection Infrared Spectroscopy (ATR)... 

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