Attenuated total quantitation

H. M. Klimisch and G. Chandra. Use of Fourier transform infrared spectroscopy with attenuated total reflectance for in vivo quantitation of polydimethylsiloxanes on human skin. J. Soc. Cosmet. Chem. Jpn. 37 73-87 (1986). 

Diffuse-reflectance MIRS has found a number of applications for dealing with hard-to-handle solid samples, such as polymer films, fibers, or solid dosage forms. Reflectance MIR spectra are not identical to the corresponding absorption spectra, but sufficiently close in general appearance to provide the same level of information. Reflectance spectra can be used for both qualitative and quantitative analysis. Basically, reflection of radiation may be of four types specular, diffuse, internal, and attenuated total. 

The primary techniques used in this study include X-ray photoelectron spectroscopy (XPS), reflection-absorption infrared spectroscopy (RAIR), and attenuated total reflectance infrared spectroscopy (ATR). XPS is the most surface-sensitive technique of the three. It provides quantitative information about the elemental composition of near-surface regions (< ca. 50 A sampling depth), but gives the least specific information about chemical structure. RAIR is restricted to the study of thin films on reflective substrates and is ideal for film thicknesses of the order of a few tens of angstroms. As a vibrational spectroscopy, it provides the type of structure-specific information that is difficult to obtain from XPS. The... 

FTIR reflectance and transmission spectroscopy is used for analysis of thin films. Nevertheless, due to the high absorptivities of mid-IR bands, the film thickness must be limited (up to 100 pm, depending on the specific bands chosen) in order to perform an accurate qualitative analysis. Other IR methods, such as attenuated total reflectance (ATR) and photoacoustic methods provide IR spectra of thick material, because they penetrate a very thin layer at the surface of a sample. However, is important to point out that the effective pathlength for the ATR and the photo-acoustic methods depends on the refractive index and thermal diffusivity, respectively. Therefore, the use of these techniques for the quantitative analysis of non-homo-geneous materials can be difficult. 

Potts, R. O., Guzek, D. B., Harris, R. R. and McKie, J. E. (1985) A noninvasive, in vivo technique to quantitatively, measure water concentration of the stratum corneum using attenuated total-reflectance infrared spectroscopy. Arch. Dermatol. Res. 277, 489-95. 

Fourier-transformed infrared spectroscopy (FT1R), either in the transmission mode(70), the grazing incidence reflection (GI) mode(7,5) or the attenuated total reflection (ATR) mode(7,2), has been the most widely used experimental tool for the characterization and structure determination of SA monolayers. GI-IR is especially useful in determining the molecular orientation in the film structures because it senses only the vibrational component perpendicular to the substrate surface(7,5). Polarized ATR-IR can also be used to study molecular orientation(7,77). McKeigue and Gula-ri(72) have used ATR-IR to quantitatively study the adsorption of the surfactant Aerosol-OT. 

Attenuated total reflectance Eourier-transform infrared (ATR-ETIR) spectroscopy is another technique recently reported to have been applied to the determination of pesticide residues on human skin and residential surfaces (Doran et al., 2000). While this technique gave good results when evaluated in the laboratory for three pesticides at 0.5 to 5 Rg/m skin loadings, field use would be very limited by the size and transportability of the instrument and the liquid-nitrogen coolant for the detector. Whatever the method, surface residues are also difficult to measure quantitatively in situ, especially on the skin. 

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). 

Nagarajan, R., Gupta, A., Mehrotra, R. and Bajaj, M.M. (2006) Quantitative analysis of alcohol, sugar, and tartaric acid in alcoholic beverages using attenuated total reflectance spectroscopy. J Aut Meth Manag Chem, 2006 (2), 1-5. 

Increasing use is being made of Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy, FTIR-ATR, as a surface sensitive method which is capable of giving quantitative... 

IR spectroscopy is one of the few analytical techniques that can be used for the characterization of solid, liquid, and gas samples. The choice of sampling technique depends upon the goal of the analysis, qualitative identification or quantitative measurement of specific analytes, upon the sample size available, and upon sample composition. Water content of the sample is a major concern, since the most common IR-transparent materials are soluble in water. Samples in different phases must be treated differently. Sampling techniques are available for transmission (absorption) measurements and, since the advent of FTIR, for several types of reflectance (reflection) measurements. The common reflectance measurements are attenuated total reflectance (ATR), diffuse reflectance or diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), and specular reflectance. The term reflection may be used in place of reflectance and may be more accurate specular reflection is actually what occurs in that measurement, for example. However, the term reflectance is widely used in the literature and will be used here. 

The challenge in FTIR quantitative analysis of polymers is the thickness of the sample. The use of peak ratios standardizes the absorbance signal and eliminates the thiekness variable. Attenuated total reflectanee (ATR) and microscope FTIR were the two methods ehosen to acquire the FTIR spectra. The filler eontent in the polymer was confirmed by ashing. 

Horowitz (1971) has discussed in detail the reagents used for detecting minute amounts of carbohydrate on paper. He has discussed separations by electrophoresis and chromatography as well as elution and quantitative collection of these substances. Wilks and Hirschfeld (1967) have discussed the practice of eluting sample spots from paper electrophoretic and paper chromatographic patterns and allowing the eluted material to fall onto the internal-reflector plate of an attenuated-total-reflection (infrared) unit (see Chap. 3). Rubner and Albers (1967) have measured the infrared absorptions of electrophoresed carbohydrates on transparent acetate film strips versus transparent strips as blanks. These workers have detected separated substances without the necessity of staining the strips. 

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