Infrared evanescent wave spectroscopy

Jakusch, M. Janotta, M. Mizaikoff, B. Mosbach, K. Haupt, K., Molecularly imprinted polymers and infrared evanescent wave spectroscopy. A chemical sensors approach, Anal. Chem. 1999, 71, 4786 1791... 

D using the same monomer and TRIM as the cross-linker [28,29]. In this case, tobacco peroxidase was used as the enzyme and the chemiluminescent reaction with luminol was used for the detection. Infrared evanescent wave spectroscopy was also used to study 2,4-D imprinted polymers prepared using 4-VPy and MMA as the... 

ECD = electron capture detector EPA = Environmental Protection Agency FEWS = fiber evanescent wave spectroscopy FID = flame ionization detection FT-IR = Fourier transform infrared GC = gas chromatography HECD = Hall electrolytic conductivity detector HRGC = high resolution gas chromatography HSD = halide-sensitive detector H2SO4 = sulfuric acid LDPE = low-density polyethylene MS = mass spectrometry NIOSH = National Institute for Occupational Safety and Health NR = not reported PI = photoionization UV = ultraviolet detection... 

An in situ method for tetrachloroethylene analysis using fiber evanescent wave spectroscopy (FEWS) has been described by Krska et al. (1993). In this method, the water flows through a glass chamber containing a silver halide fiber coated with low-density polyethylene in an amorphous phase. The coating serves to concentrate the tetrachloroethylene, and the compound is detected using infrared spectrophotometry. The detection limit of this method, which was validated using headspace GC, was 1 ppm. 

Raichlin Y. Katzir A. (2008). Fiber-Optic Evanescent Wave Spectroscopy in the Middle Infrared. Applied Spectroscopy, Vol.62, No.2, p>p. 55A-72A, ISSN 1943-3530 Rappoport, Z. Marek, I. (2004). The chemistry of organolithium compounds, Wiley, ISBN 0-470-84339-X, Chichester... 

ATR has been found as an easy to use, non-destmctive and surface-sensitive IR sampling technique for the in situ investigation of CMP processes (Hind et al., 2001). It was initially pushed by Harrick (1967) and comprehensively treated in his early book and following editions together with Mirabella (1985). Numerous alternative and partially deceptive names are used instead of ATR spectroscopy internal reflection spectroscopy, evanescent wave spectroscopy, frustrated total internal reflection (FTIR, which should not to be confused with Fourier-transform infrared spectroscopy) and multiple internal reflection (MIR, which should not to be confused with mid-infrared )- Therefore, in the following the term ATR as defined in Section 14.4.1 and illustrated with Figure 14.8 is used exclusively. 

Wise and co-workers used an infrared (IR) evanescent wave spectroscopy technique to follow the disappearance of a tracer of deuterated 1,4-polybutadiene (PBDE) displaced in a channel by unlabeled PBDE of the same molecular weight. Linear PBDE is a convenient polymer for experimental research because it flows at room temperature and has a viscosity that is relatively insensitive to shear rate. One face of the channel was fabricated from a ZnSe IR crystal, and the deuterated polymer was placed on the surface. The deuterated polymer was then allowed to equilibrate with hydrogenated polymer of the same molecular weight, and flow was initiated. The concentration of deuterated polymer in the wall region after the... 

Sensing Infrared Fiber Evanescent Wave Spectroscopy... 

Anne M. L., La Salle E. L., Bureau B., Tristan J., Brochot E, Boussard-Pledel C., Ma H. L., Zhang X. H., and Adam J. L., Polymerisation of an industrial resin monitored by infrared fiber evanescent wave spectroscopy. Sens, Actuators, B, 137, 687-691 (2009). 

Li K. and Meichsner J., In situ infrared fibre evanescent wave spectroscopy as a diagnostic tool for plasma potymerization in a gas discharge,/ Phys, D AppI, Phys, 34,1744-1744 (2001). 

Anne M. L., Le Lan C., Monbet V., Boussard-Pledel C., Ropert M., Sire 0., Pouchard M., Jard C., Lucas J., Adam J. L., Brissot R, Bureau B., and Loreal 0., Fiber evanescent wave spectroscopy using the mid-infrared provides useful fingerprints for metabolic profiling in humans, J. Biomed. Opt, 14(2009). 

A fiber-optic device has been described that can monitor chlorinated hydrocarbons in water (Gobel et al. 1994). The sensor is based on the diffusion of chlorinated hydrocarbons into a polymeric layer surrounding a silver halide optical fiber through which is passed broad-band mid-infrared radiation. The chlorinated compounds concentrated in the polymer absorb some of the radiation that escapes the liber (evanescent wave) this technique is a variant of attenuated total reflection (ATR) spectroscopy. A LOD for chloroform was stated to be 5 mg/L (5 ppm). This sensor does not have a high degree of selectivity for chloroform over other chlorinated aliphatic hydrocarbons, but appears to be useful for continuous monitoring purposes. 

Quantitative determinations of the thicknesses of a multiple - layered sample (for example, two polymer layers in intimate contact) by ATR spectroscopy has been shown to be possible. The attenuation effect on the evanescent wave by the layer in contact with the IRE surface must be taken into account (112). Extension of this idea of a step-type concentration profile for an adsorbed surfactant layer on an IRE surface was made (113). and equations relating the Gibbs surface excess to the absorbance in the infrared spectrum of a sufficiently thin adsorbed surfactant layer were developed. The addition of a thin layer of a viscous hydrocarbon liquid to the IRE surface was investigated as a model of a liquid-liquid interface (114) for studies of metal extraction ( Ni+2, Cu+2) by a hydrophobic chelating agent. The extraction of the metals from an aqueous buffer into the hydrocarbon layer was monitored kinetically by the appearance of bands unique to the complex formed. 

This article shows how the evanescent wave can be used with advantage for spectroscopic purposes in the field of biomedical engineering. Three types of spectroscopy can be done with the evanescent wave in the UV-VIS range of the spectrum (a) attenuated total reflection (ATR) spectroscopy, which is well known in the infrared (b) the excitation of Raman scattering with the evanescent wave and (c) the excitation of fluorescence with the evanescent wave. The first two types will be discussed in this article the third is discussed for example by Hirschfeld U) and more recently by Watkins and Robertson (2). But before going into details a historical review may be of some interest. 

Internal reflection spectroscopy (2), also known as attenuated total reflectance (ATR), is a versatile, nondestructive technique for obtaining the IR 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. The technique goes back to Newton who, in studies of the total reflection light at the interface between two media of different retractive indices, discovered that an evanescent wave in the less dense medium extends beyond the reflecting interface. Infrared spectra can conveniently be obtained by measuring the interaction of the evanescent wave with the external less dense medium. 

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. 

If sample material is in contact with the totally reflecting surface of the prism, an evanescent wave in the sample extends beyond the reflecting interface and the evanescent wave will be attenuated in infrared regions.The intensity of this wave decays exponentially with the distance from the surface of the ATR crystal. Due to the fact that the electromagnetic field passes only a few micrometers of the sample, this method is insensitive to sample thickness and therefore useful for analysis of strong absorbing or thick materials. Influencing factors for FT-ATR-IR-spectroscopy are as follows ... 

With attenuated total reflection spectroscopy, the light absorption by the electrolyte solution and the cell window is no obstacle. The probe beam enters a crystal transparent for infrared light. It is directed to the outer surface of the crystal, which is coated with a thin layer of the electrode material under investigation. The beam is reflected, but a small part (the evanescent wave) penetrates the surface and thus can probe species located immediately on the electrode surface. The returning beam contains exactly this information. As discussed below (p. 91) in detail, this approach shows also serious limitations. 

In ATR, a beam of infrared light is totally reflected inside a specially cut infrared transparent material that has a high index of refraction. Typical materials used for ATR prisms are Ge, Si, and ZnSe. Because the index of refraction differs between the polymer and the prism, an evanescent wave penetrates the polymer if it intimately contacts the prism. The infrared radiation will interact with molecular vibrations in the same manner as in conventional infrared spectroscopy. The amplitude of the evanescent wave decays exponentially from the surface, so the depth of penetration is arbitrarily taken as the point where the amplitude decays to 1/e (37%) of its initial value. The depth of penetration depends on the ratio of the refractive indices between the polymer and the prism, the angle of incidence, and frequency of radiation in the following manner (Ishida, 1987) ... 

The penetration depth of the evanescent wave into the electrolyte for in situ ATR infrared experiments is generally taken as ca. X/10 on this basis, in the region of the O—H stretch of liquid water, s = 55 mol dm cm [42], an absorbance of <0.1 would be expected, and this is the essence of the application of ATR techniques in in situ infrared spectroscopy. 

When light traversing an optically dense medium approaches an interface with a more optically rare medium at an angle exceeding a critical value, Bent = sin (rerare/ dens), total internal reflection occurs and an evanescent wave of exponentially deca5ung intensity penetrates the rarer medium. This phenomenon is at the heart of certain spectroscopic methods used to probe biomolecules at interfaces (199). In total internal reflection fluorescence (TIRF) spectroscopy (200-202), the evanescent wave excites fluorescent probes attached to the biomolecules, and detection of the emission associated with their decay provides information on the density, composition, and conformation of adsorbed molecules. In fourier transform infrared attenuated total reflection (FTIR-ATIR) spectroscopy (203,204), the evanescent wave excites certain molecular vibrational degrees of freedom, and the detected loss in intensity due to these absorbances can provide quantitative data on density, composition, and conformation. 

Abstract This chapter describes recent breakthroughs in the instrumentation for far-ultraviolet (FUV) spectroscopy. The key technique is attenuated total reflection (ATR) that is frequently used in the infrared region. ATR technique decreases the absorbance of samples with strong absorptivity because of the penetration depth of the evanescent wave less than 100 nm. Therefore, ATR-FUV spectroscopy realizes the measurement of FUV spectra of samples in liquid and solid states. Some applications (in-line monitoring, characterization of polymers and time-resolved spectroscopy in sub-microsecond) are introduced in terms of instrumentation. This chapter explains not only the detail of the instruments but also the mathematical correction for ATR spectra to separate the absorption and refraction indices. 

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