Attenuated total reflection sample contact

The attenuated total reflectance (ATR) technique is used commonly in the near-infrared for obtaining absorption spectra of thin Aims and opaque materials. The sample, of refractive index i, is placed in direct contact with a material which is transparent in the region of interest, such as thallium bromide/thallium iodide (known as KRS-5), silver chloride or germanium, of relatively high refractive index so that Then, as Figure 3.f8... 

Attenuated Total Reflection (ATR).4c A sample brought in contact with the totally reflecting surface of a high-refractive-index material (the ATR crystal), will, on IR irradiation, give an evanescent wave in the less dense medium that extends beyond the reflecting interface. This wave will be attenuated in regions of the IR spectrum where the sample absorbs energy. Observation of such waves constitute ATR measurements. Only the small amounts of beads necessary to cover the area of the ATR crystal are required. 

Attenuated total reflection FTIR is a well-established technique for obtaining absorbance spectra of opaque samples. The mode of interaction is unique because the probing radiation is propagated in a high index-of-refraction internal reflection element (IRE). The radiation interacts with the material of interest, which is in close contact with the IRE, forming an interface across which a nonpropagating evanescent field penetrates the surface of the material of interest to a depth in the order of one wavelength of the radiation. The electric field at the interface penetrates the rarer medium in the form of an evanescent field whose amplitude decays exponentially with distance into the rarer medium. 

Attenuated Total Reflectance This method can be used to identify solid drugs but is only of use where relatively large amounts of compounds are available. The finely-ground sample is spread as a thin layer onto the sticky side of a piece of self-adhesive tape, and the tape is placed against the reflecting surface of the instrument with the sample side in contact. Sufficient sample is required to cover the surface of the tape completely, otherwise the spectrum of the tape will be recorded in addition to that of the sample. The technique is of use when the acid and salt forms need to be differentiated. 

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). 

Attenuated total-reflectance (ATR) spectroscopy is a widely used sampling technique, in which a sample is placed in contact with a reflecting medium (a plate or prism shaped material called an internal reflectance element). A beam of radiation entering the prism is reflected internally if the angle of incidence at the interface between sample and prism is greater than the critical angle (a function of the refractive index of the sample and the prism). 

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). 

Figure 10.17 Devices allowing the study of samples by reflection, (a) Schematic representation of two ATR devices (attenuated total reflection) a model with a trapezium crystal for multiple reflections and a model for single reflection with solid microsamples (the application of a weight improves the contact of the sample with the crystal s rounded form). Basic formula and notion of critical angle (h) Specular reflection device. Optical pathway of the apparatus at a fixed angle of 30 ° for highly reflecting samples and of 60 ° for the contrary (c) Optical scheme for a diffuse reflection device and diagram of a Spectra Tech model.

Figure 1 Attenuated Total Reflection accessory for FTIR spectrometer with diamond crystal through which infrared beam is reflected (upper). Plastic samples must have good contact with the surface of the diamond to obtain well-resolved spectra (lower)...

Reflectance techniques can be used for samples which are difficult to analyse by normal transmittance methods. Reflectance methods can be divided into two categories internal reflectance measurements can be made by using an attenuated total reflectance (ATR) ceil in contact with the sample, while there are also external reflectance measurements which involve an infrared beam being reflected directly from the sample surface. 

Fig. 4.26. ATR-rod (attenuated total reflection) monitoring changes in the sample via multiple tc4al reflection and evanescent fields in the reaction solution. Fibers are hooked to a highly optically polished glass, in which the radiation is guided in contact with the solution in the...

ATR-FTIR spectroscopy (attenuated total reflectance Fourier transform infrared spectroscopy)—IR spectroscopy uses the absorption of infrared radiation to probe the vibrational frequency of molecular motions. Attenuated total reflectance method uses a crystal of high refractive index to channel the infrared light (using total internal reflectance) into the crystal and causes only a thin layer of a sample in contact with the exterior of the crystal to be sensitively detected. 

Attenuated total-reflectance (ATR) IR spectroscopy represents another solid-state sampling technique. Here the samples are placed in close contact to a crystal that is transparent in the IR region. This technique provides only spectral information about the sample surface in direct contact with the ATR crystal and is thus applied in the characterization of coatings rather than in bulk material. 

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