Diffuse-reflectance spectroscopy applications

The application of diffuse reflectance spectroscopy to the chemistry of transition metal coordination compounds. E. L. Simmons, Coord. Chem. Rev., 1974,14,181-196 (81). 

Until quite recently the very initial stages of metal deposition were difficult to characterize in detail by structure- and morphology-sensitive techniques. As a consequence and for practical purposes - multilayers were more useful for applications than monolayers - the main interest was focussed onto thick deposits. Optical and electron microscopy, ellipsometry and specular or diffuse reflectance spectroscopy were the classic tools, by which the emerging shape of the deposit was monitored [4-7],... 

V. APPLICATIONS OF DIFFUSE REFLECTANCE SPECTROSCOPY TO THE STUDY OF PHARMACEUTICAL SOLIDS 42... 

Although UV/VIS diffuse reflectance spectroscopy has not been used extensively in the study of pharmaceutical solids, its applications have been sufficiently numerous that the power of the technique is evident. The full reflectance spectra, or the derived colorimetry parameters, can be very useful in the study of solids that are characterized by color detectable by the human eye. It is evident that questions pertaining to the colorants used for identification purposes in tablet formulations can be fully answered through the use of appropriately designed diffuse reflectance spectral experiments. With the advent of newer, computer-controlled instrumentation, the utility of UV/VIS diffuse reflectance as a characterization tool for solids of pharmaceutical interest should continue to be amply demonstrated. 

Diffuse reflectance spectroscopy has been widely used to characterize the surface of solids as well as films and coatings present on a solid substrate (6). The application of this technique to the study of adsorbed species has been much more limited (26) and, thus far, has not involved the use of FT spectroscopy. 

Second derivative pre-treatment is rather common in NIR diffuse reflectance spectroscopy. This treatment results in the removal of both baseline offset differences between spectra and differences in baseline slopes between spectra. Its historical effectiveness in NIR reflectance applications suggests that baseline slope changes are common in these applications, although there is no theoretical basis for such variations. 

Ferraro JR, Basile LJ (1978) Fourier transform infrared application to national problems In Ferraro JR, Basile U (eds) Fourier transform infrared spectroscopy - applications to chemical systems, Vol 4 Academic Press, New York, 275-302 Ferraro JR, Rein AJ (1985) Application of diffuse reflectance spectroscopy in the far-infrared region In Ferraro JR, Basile LJ (eds) Fourier transform infrared spectroscopy -applications to chemical systems, Vol 4 Academic Press, New York, 244-282 Frank IE, Feikema J, Constantine N, Kowalski BR (1984) Prediction of product quality from spectral data using the partial least squares method J Chem Inf Comput Sci 24 20-24 Fuller MP, Griffiths PR (1980) Infrared microsampling by diffuse reflectance Fourier transform spectrometry Appl Spectrosc 34 533-539... 

Ferraro JR, Nakamoto K (1994) Introductory Raman Spectroscopy, Academic Press, New York Ferraro JR, Rein AJ (198.5) Applications of Diffuse Reflectance Spectroscopy in the Far-Infrared Region. In Ferraro JR, Basile LJ (eds) Fourier Transform Infrared Spectroscopy, vol 4. Academic, Orlando... 

The simultaneous application of EPR/ultraviolet-visible diffuse reflectance spectroscopy (UV-vis-DRS)/online gas chromatography (GC) to characterize working catalysts was realized a few years ago 14), and laser-Raman spectroscopy has recently been coupled with these to provide the first such simultaneous application of three techniques 15). 

A typical example of the characterization of a polymorphic system by FT Raman spectroscopy has been given by Gu and Jiang (1995) while an application of the technique with near infrared excitation to the polymorphic cimetidine system has been described by Tudor et al. (1991). The FT Raman technique has been compared to infrared diffuse reflection spectroscopy in the study of the polymorphs of spironolactone (Neville et al. 1992), and the pseudopolymorphic transition of caffeine hydrate (i.e. loss of solvent) has been monitored using the technique (de Matas et al. 1996). 

Diffuse reflectance spectroscopy has found wide application for the characterization of supported transition-metal ions that are the normal precursors of supported metals. It, therefore, can be used to detect unreduced transition metal ions (57a,c, 186, 216-221). 

S. Yoshioka, K. Kimura, H. Ogata, T. Shibazaki, and A. Ejima, Application of diffuse reflectance spectroscopy to stability test of solid dosage forms [in Japanese], Yakuzaigaku 39,75-82(1979). 

The applicability of the Pt deposition precipitation technique (DP) on mesoporous silica has been evaluated and discussed. A detailed synthesis procedure is given, and a suitable support from the SBA-15 family has been identified. The material synthesized at the conditions described here was clearly able to withstand the severe conditions of the DP treatment, indicating improved hydrothermal stability. The incorporation of the active species was accomplished without compromising the structural integrity of the parent material, as monitored by XRD and N2-sorption measurements. Using UV-Vis diffuse reflectance spectroscopy we were able to detect the platinum surface complex that coexists with platinum nanoparticles on the impregnated solid. 

For a discussion of reflectance spectroscopy, two types of reflectance must be defined, specular and diffuse. Specular reflectance is simply mirrorlike reflectance from a surface and is sometimes called regular reflectance it has a well-defined reflectance angle. Diffuse reflectance is defined as reflected radiant energy that has been partially absorbed and partially scattered by a surface with no defined angle of reflectance. The diffuse reflectance technique is widely used today for industrial applications involving textiles, plastics, paints, dyestuffs, inks, paper, food, and building materials. In the area of basic research, diffuse reflectance spectroscopy has been used in studies of solid-solid reactions, of species absorbed on metal surfaces, of radiation transfer, and of slightly soluble species. 

Diffuse Reflectance Spectroscopy A third technique for the study of solids by FT-IR is diffuse reflectance spectroscopy. The technique which was recently described by Fuller and Griffiths, (33, 34) allows good quality spectra to be obtained on neat powdered samples. The technique requires fine grinding of the samples so, in this aspect, it is more restrictive than PAS but is substantially faster than PAS so is applicable to following reactions. Fig. 3 compares spectra for a Pittsburgh seam coal using the three techniques. 

Diffuse reflectance spectroscopy (DRS) has been frequently employed in UV-Vis spectroscopy of zeolites (cf. Volume 4, Chapter 4 of the present series). More recently, it became also popular in IR investigations (cf., e.g., [160, 161]). The DRIFT technique is advantageous because it is successfully applicable not only in the mid infrared but also in the near infrared (NIR) region of 4000-10,000 cm where the transmission technique usually fails because of severe scattering through the absorbent particles. The NIR range, however, is very important with respect to the study of overtone and combination modes of vibrations. Moreover, diffuse reflectance IR experiments can be carried out not only with pressed wafers as in transmission spectroscopy, but also with zeolite pow-... 

The formation of Yb and of Eu " in CaO has been established in diffuse reflectance spectroscopy experiments. Interest in these materials, which were produced by the reduction of M2O3 with Ca vapour, arises from their application as laser or photochromic materials. ... 

Diffuse reflectance spectroscopy is a versatile tool that allows us to accurately measure the flux per wavelength of light reflected in a scattered manner from a sample. Whether the sample be almost purely diffuse, as in a lightly packed powder, predominately specular, as in a burnished metal surface, or something in between, such as a glossy paint sample, diffuse reflectance spectroscopy tells much about the physical and chemical characteristics that are not available by other analytical means. In addition, diffuse reflectance spectroscopy in the visible region of the spectrum— that area between approximately 360 and 760 nm where our eyes are sensitive— allows quantitation of color measurement for biological, pharmaceutical, commercial, and artistic applications. 

Blanco, C., P. Casado, and A. Poza, Application of diffuse reflectance spectroscopy. It s application to the determination of powder milk composition, Quim. Ind. Madrid), 26 361-363 (1980) (in Spanish). 

Successful application of NIRS greatly depends on the robustness, specificity, selectivity and transferability of the calibration. In particular, it is highly desirable to be able to support a plant analyser from a laboratory instrument. Sampling-based optical artefacts and the optical characteristics of each instrument, including mechanical and photometric errors, impair transferability of data between instruments. Collaborative NIRS projects with transfer between instruments of calibration files, equations and spectra have been described [245] and interlaboratory collaborative studies of NIRS calibration methodology (for moisture analysis) have been carried out [246]. Blanco et al. [247] have compared various calibration methods in NIR diffuse reflectance spectroscopy. An absolute procedure for instrument calibration and standardisation has been presented [248]. A cloning procedure and... 

NIRS in internal reflection mode has also been used to study in situ low-level surfactant adsorption reactions (sub-monolayer coverage) using reactive internal reflection elements [175]. Standard errors of 0.04% were reported for the determination of 0.25-1.25% additives in nylon (cubes and films) [294]. Turley et al [309] used NIRS to determine ethylene oxide content and glycerin additive concentrations in ethylene oxide/propylene oxide copolymers. NIR diffuse reflectance spectroscopy was used to analyse up to 10% paper (cellulose) in agglomerate plastic waste (PE 60%, PS 20%, PP 15%, PVC 4%) [161]. For pigment applications, cfr, ref. [310]. 

---