Microspectroscopic method

Microspectroscopy. In situ spectroscopic methods are essential to a fundamental understanding of catalytic reactions, thanks to their ability to unravel useful structure-function relationships. However, most of these techniques average information over the whole catalyst sample, whereas in many cases it is of utmost importance to probe distinct areas of catalyst particles or grains to reveal how the structural features render into catalytic function. For this purpose, microscopic methods may be of assistance. The following section lists the examples of application of in situ microspectroscopic methods in catalysis. 

Microspectroscopic Method for Kinetic Measurements at High Temperatures and High Pressures Applied Spectroscopy 38, 680-686. 

Since the introduction ofvibrational microspectroscopic methods into the applied sciences in the early 1990s, agricultural crops stood under intensive investigation. 

The high potential of nondestructive microspectroscopic methods is represented by the increasing number of recent publications, dealing with the uptake and metabolism of environmental contaminants and crop protection products. 

The big advantages of vibrational microspectroscopic methods become clearly apparent when studying plant-pathogen interactions. 

R. Bhargava and I. W. Levin, Recent developments in Fourier transform infrared (FTTR) microspectroscopic methods for biomedical analyses from single-point detection to two-dimensional imaging, in Biomedical Photonics Handbook, T. Vo-Dinh, Ed., CRC Press, Boca Raton, FL, 2003, p. 1. 

Since the theoretical background and practical implementation of vibrational spectroscopy are described elsewhere in this encyclopedia, the emphasis here will be on the extension of Raman and infrared spectroscopy to the microscopic realm. It should be noted that many of the methods described here are applicable to other microspectroscopic methods, especially those based on optical phenomena such as fluorescence. 

Carter et al. [402] have addressed the chemical assessment of automotive clearcoats (usually melamine-cross-linked systems), which requires evaluation of the cross-linker type, HALS and UV absorbers. Coating systems require a variety of chemical analytical techniques for their evaluation [403], including UV microspectroscopy [402, 404], /xFTIR [402,405], /xRS [406,407], NMR [408], ESR [409], ToF-SIMS [410,411] and hydroperoxide titration [412]. Ideally, what is needed for industrial evaluation purposes is a set of techniques that can follow chemical changes in individual layers of a full automotive paint system, typically consisting of 45 /xm clearcoat, 25 /xm basecoat, 35 /xm primer, and 35 /xm E-coat on metal. The clearcoat must shield underlayers from UV. Unlike the case for IR radiation, examination of 30 /xm and thinner clearcoat layers with 0.3 to 0.4 /xm radiation lends itself quite well to the use of microscopes and microspectroscopic techniques. UV microspectroscopy of 10 /xm paint system cross-sections is the method of choice cfr. also Chp. 1.1). UV microspectroscopy... 

In concluding Section 16.5, it is worth mentioning that the gradient-shaving method is now a commonly used technique for depth-profile analysis, and that not only the transmission and specular-reflection methods but also the ATR method is frequently used for such infrared microspectroscopic measurements. 

In order to enhance spatial resolution, it is necessary to make the NA of the objective larger, as is clear from Equation (17.3) that is, either n or 6, or both of them should be increased. Due to the optical geometry of a microscope, there is an upper limit for 0. On the other hand, it is possible practically to increase n by introducing an attenuated total reflection (ATR) accessory into a microscope (see Chapter 13 for the ATR method this is a frequently used accessory for many recent infrared microspectroscopy absorption measurements). The refractive index n of Ge, which is a commonly used material for an internal reflection element (IRE) in the ATR method, is about 4, and the NA when using a Ge IRE exceeds 2. This means that, if an ATR accessory with a Ge IRE is combined with a microscope, the theoretical spatial resolution is enhanced about four times that of the conventional reflection measurement. In fact, in the FT-IR microspectroscopic imaging measurement with a Ge ATR accessory, it has been confirmed that a spatial resolution comparable to the infrared wavelength used for the measurement is realized, and thus a higher spatial resolution may be attainable. 

To exploit such advantages, combinations of the ATR method and microspectroscopic imaging methods have been developed, and in recent years ATR microscopic imaging is utilized much more frequently. 

Infrared and Raman instrumental advances, microspectroscopic techniques and fibre optics and new sampling methods have made possible many biological and medical applications. Correction for background and interference is automatically performed by most modern instruments. The use of statistical techniques and of derivative spectra for the examination of subtle differences in cases where bands overlap have been very useful. The direct examination of cells and tissues by infrared " can provide useful information on cellular composition, packing of cellular components, cell structure, metabolic processes and disease. Near infrared and Fourier Transform techniques may be applied to the study of food. ... 

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