Fourier transform infrared penetration depth

The use of infrared spectroscopy in the Earth and environmental sciences has been widespread for decades however, until development of the attenuated total reflectance (ATR) technique, the primary use was ex situ material characterization (Chen and Gardella, 1998 Tejedor-Tejedor et al., 1998 Degenhardt and McQuillan, 1999 Peak et al., 1999 Wijnja and Schulthess, 1999 Aral and Sparks, 2001 Kirwan et al., 2003). For the study of environmental systems, the strength of the ATR-Fourier transform infrared (FTIR) technique lies in its intrinsic surface sensitivity. Spectra are collected only from absorptions of an evanescent wave with a maximum penetration depth of several micrometers from the internal reflection element into the solution phase (Harrick, 1967). This short optical path length allows one to overcome any absorption due to an aqueous phase associated with the sample while maintaining a high sensitivity to species at the mineral-water interface (McQuillan, 2001). Therefore, ATR—FTIR represents a technique capable of performing in situ spectroscopic studies in real time. 

Micro-Fourier transform infrared (FT-IR) spectroscopy was employed to examine the chemical structures by observing absorption bands at 1716 cm 1 (carbonyl group), 964 cm"1 (trans- inylene) and 910 cm 1 (end-vinyl). After 2 months from the irradiation, samples were sliced into 100-150 pm films along the direction of ion-beam penetration and the FT-IR spectra were measured as a function of depth from the surface [6]. We obtained the net absorbance AAbs. for the three bands for carbonyl group, /raws-vinylene and end-vinyl at each depth by subtraction of the measured spectrum from that of the unirradiated sample. Sliced samples were stored in the dark at room temperature. They were repeatedly measured after 4, 6 and 12 months from the irradiation to observe the effect of long-term storage. 

Wessel, E. et al. (2006) Qbservation of a penetration depth gradient in attenuated total reflection Fourier transform infrared spectroscopic imaging applications. Appl. Spectrosc., 60 (12), 1488-1492. 

Fourier transform infrared speetroseopy (FTIR) in the mode of attenuated total re-fleetion (ATR) has been sueeessfully applied for studying polymer adsorption or exehange on the surfaee of an infrared prism eonsisting of, e.g., germanium or sil-ieon [44, 45]. In an ATR eell a beam of light is totally refleeted at the boundary of the interfaee between the prism and the solution. The prism has a refraetive index higher than that of the solution. An evaneseent wave penetrates the medium of lower refraetive index (polymer solution side) with a penetration depth of the order of the... 

ATR spectroscopy in the infrared has been used extensively in protein adsorption studies. Transmission IR spectra of a protein contain a wealth of conformational information. ATR-IR spectroscopy has been used to study protein adsorption from whole, flowing blood ex vivo 164). Fourier transform (FT) infrared spectra (ATR-FTIR) can be collected each 5-10 seconds165), thus making kinetic study of protein adsorption by IR possible 166). Interaction of protein with soft contact lens materials has been studied by ATR-FTIR 167). The ATR-IR method suffers from problems similar to TIRF there is no direct quantitation of the amount of protein adsorbed, although a scheme similar to the one used for intrinsic TIRF has been proposed 168) the depth of penetration is usually much larger than in any other evanescent method, i.e. up to 1000 nm water absorbs strongly in the infrared and can overwhelm the protein signal, even with spectral subtraction applied. 

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