Attenuated multiple total internal reflection technique

The second case refers to the so-called Internal Reflection Spectroscopy, that is used in the so-called Attenuated Multiple Total Internal Reflection technique... 

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.. 

Attenuated total reflection (ATR) has grown into the most widely practiced technique in infrared spectrometry. The reasons for this are fairly straightforward the technique requires little or no sample preparation, and consistent results can be obtained with relatively little care or expertise. The technique is not foolproof, but it can be very forgiving. ATR spectrometry is known by a number of alternative names, for example, multiple internal reflection (MIR), which is not to be confused with mid-infrared, frustrated multiple internal reflection (FMIR), evanescent wave spectrometry (EWS), frustrated total internal reflection (FTIR), which is not the same as Fourier transform infrared (FT-IR) spectrometry, and internal reflection spectrometry (IRS), but IRS is better known, at least in the United States, as the Internal Revenue Service. 

The ATR or attenuated total reflectance also known as MIR or multiple internal reflectance) technique is a powerful method for the study of tlje spectra of surfaces. The technique can also be used in cases when only a small thickness of the material under study such as a thick polymer plate or aqueous solution is to be sampled. The samples studied by the ATR technique can be free standing films, coatings on metals or other substrates, powders or liquids. The ATR technique was originally developed by Fahrenfort (3) and has been thoroughly reviewed by Harrick (4). The ATR technique is briefly reviewed here. 

Solid state spectra can be measured by the Attenuated Total Reflectance or Multiple Internal Reflection methods as well as by simple transmission techniques (222). Brooker (223) has reported the discovery of the translational vibrations of NaN02, NaNOs, and CaCOs (calcite). The orientation of the bonds in (U02)(N0s)2. 6 H2O has been ascertained from the spectra obtained in this manner (223). 

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. 

IR spectroscopy is a common analytical technique in the textile industry. IR is capable of identifying fibers and their additives, as well as showing quantitative blend ratios and additive contents. The ATR (attenuated total reflection) technique, especially in its multiple form, MIR (multiple internal reflection) is of special importance in this field. The sample preparation is simple and fast the cut out swatches with appropriate surface areas are placed against each side of the MIR crystal, ensuring sufficient and uniform contact across the crystal surface. The internal reflection methods are non-destructive, so that the sample may be saved for other types of analysis, they are, further, methods of surface analysis. This is advantageous in all cases where the finish resides primarily on the fiber surface. In this case, a very strong spectrum of the finish is obtained, with minimal interference from the base fiber (Hannah et al., 1975). 

Good results in the IR spectroscopy of aqueous samples are given by the ATR technique (attenuated total reflection) and a further development of this, the MIR technique (multiple internal reflection) a prerequisite is that the sample space of the IR spectrophotometer is sufficiently large to accommodate the supplementary MIR device. The MIR technique likewise involves measurement of the absorption spectrum of the substance. All of the same molecule-specific and analytical conclusions can therefore be drawn as with an IR spectrum in the transmission of the same substance, even though the two spectra are physically not quite identical. 

Internal reflection spectroscopy, also known as attenuated total reflectance (ATR) or multiple internal reflectance (MIR), is a versatile, nondestructive technique for obtaining the infrared 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. 

Sampling systems based on the multiple internal reflection (MIR) technique, also called attenuated total reflectance (ATR) spectroscopy [916], are very useful for the study of polymer surface degradation [476,1437]. 

ATR. Attenuated total reflectance and its extension, frustrated multiple internal reflectance (FMIR), are excellent techniques for the analysis of surfaces. In these techniques the sample does not have to be reflecting, as the reflection is done by the crystal-sample interface (Section 3.8). 

Attenuated Total Reflection, Multiple Internal Reflection and Other Reflection Techniques... 

If the sample has a smooth, planar surface so that good physical contact with an infrared-transparent, higher refractive index prism/plate may be achieved, it can be examined by an infrared reflection technique, for example, one using attenuated total reflection, multiple internal reflection. It should be borne in mind, when examining polymeric films, that the sample may be a laminate and hence examination may give very different spectra from reflection at the two surfaces and also from transmission techniques. A coating or paint may be directly applied to a transparent plate for transmission or reflection techniques. 

Basic Techniques - Liquid, Solution, Dispersion Dispersive Techniques Films, Solvent Cast, Hot Press. Microtome Attenuated Total Reflection, Multiple Internal Reflection and Other Reflection Techniques Pyrolysis. Microscope, etc. 

Electromoduiated Infrared Spectroscopy. The form most widely in use is the electromoduiated attenuated-total-reflection-spectroscopy. This is the electromoduiated form of the multiple internal reflection spectroscopy that was previously discussed. The practice here is to modulate, by switching the potential between two values, and monitor the absorption changes by lock-in techniques. Description of this technique with an emphasis on metal-electrolyte interfaces can be found in (70). The modulation here is different from all the other techniques that were mentioned in the sense that the modulation is not a small perturbation of an equilibrium state but a shift between two equilibrium states. Whether... 

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