Grazing-angle reflectance spectroscopy

Figure 11 The Spectra-Tech FT-80 grazing angle accessory. A typical accessory for grazing angle reflectance spectroscopy. A polarizer that transmits only P polarized incident light improves the sensitivity of the measurement.

FTIR spectroscopy can be used in diffuse reflectance, specular reflectance, and external reflectance in grazing angle reflectance mode [23]. It enables the analysis of functional group and specific bonds of surface species. Particles can be measured separately (diffuse reflectance mode) after being scraped from composite electrodes [24]. 

It is recommended to prepare electrodes comprising only A1 foil and the active mass— particles embedded by light pressnre into soft A1 foil electrodes. Such electrodes can be polarized, cycled, and then measnred by FTIR spectroscopy (reflectance modes such as grazing angle reflectance or specular reflectance modes in which there are commercial accessories available), Raman, and XPS. 

Optical models of the interaction of polarized radiation with plane parallel layers are based on Maxwell s equations. Many derivations have ajqieared in the literature. The most generalized models treat the probed material as an n-layered system with an arbitrary variation in optical properties with distance. Optical modeling was first applied to an isotropic monolayer deposited on an aqueous subphase by Dluhy (25). In this work, it was established that when the optical constants of the substrate are lower than the monolayer, non-zero electric field intensities exist in three dimensions, unlike the cases of grazing-angle reflection from metal surfaces or normal transmission spectroscopy. 

Masuko, M., Toda, Y. and Suzuki, A., Grazing-angle reflection FT-IR spectroscopy of adsorbed molecular films on the rubbed steel surface. Proc. Intern. Trib. Conf, Nagasaki, Oct. 2000, pp. 493-497. publ. JST, Tokyo. 

Reflection-Absorption IR spectroscopy (RAIRS) where the linearly polarized IR beam is specularly reflected from the front face of a highly reflective sample, such as a metal single crystal surface (Figure 3.1(a)). This is also sometimes referred to as IRAS (IR reflection absorption). The IR beam comes in at grazing angle (i.e. almost parallel to the surface), and although absorption bands in RAIRS have intensities that are some two orders of magnitude weaker than in transmission studies on... 

Other recent applications of FT-IR in pharmaceutical analysis include reaction monitoring by fiberoptic FT-IR/ATR spectroscopy140 and stability studies of pharmaceutical emulsions using FT-IR microscopy.141 A novel equipment cleaning verification procedure using grazing angle fiberoptic FT-IR reflection-absorption spectroscopy was described by Perston et al.142... 

B.B. Perston, M.L. Hamilton, B.E. Williamson, PW. Harland, M.A. Thomson and P.J. Melling, Grazing-angle fiber-optic Fourier transform infrared reflection-absorption spectroscopy for in situ detection and quantification of two active pharmaceutical ingredients on glass. Anal. Chem., 79, 1231-1236 (2007). 

GATR Grazing-angle attenuated total reflecTance infrared specTroscopy... 

Reflection-absorption (RA) or grazing-angle spectroscopy, is a very useful technique that gives information about the direction of transition dipoles in a sample. Figure 3 present an optical setup for a grazing-angle experiment (22). 

A modification of the simple grazing-angle experiment is the multiple reflection -absorption spectroscopy, which was first described by Gaines (Figure 6) (24). It has a unique value for the detection of order-disorder transformations in the structure of a... 

Very thin films (monolayer or multilayer) can be studied by IR spectroscopy, provided that the IR beam crosses a reasonably large fraction of the monolayer this can be done by (i) grazing-angle techniques (whereby the IR beam angles of incidence and reflection are of the order of 1° to 3°) or (ii) multiple internal reflections of the IRbeam inside the monolayer (infrared reflectance and absorbance spectroscopy (IRRAS). Fig. 11.19 shows the chemical structure of an analyte (Fullerene-fcz s-[ethylthio-tetrakis(3,4-dibutyT2-thiophene-5-ethenyl)-5-bromo-3,4-dibutyl-2-thiophene] malonate),... 

Reflection-Absorption Infrared Spectroscopy (RAIS) operating at the grazing-angle which is one of the most powerful resonance absorption phenomenon and is the most sensitive optical absorption technique available for measuring low concentrations of chemical componnds adhered to surfaces and even allows for the non-destractive mono layer chemical analysis on the surface. Figure 6 shows the FOC-GAP-FTIR spectra 5 and 10 ug/cm 2-CEES deposited as a trace residue on stainless steel surface. It is clear from the spectra shown that low limits of detection (LOD) achievable could be as low as nanograms/cm (milligrams/m ). 

---