X-ray analysis methods

Figure I. Schematic illustrations of microfocus synchrotron X-ray analysis methods (a) small-angle X-ray scattering (SAXS) (b) microfocus X-ray diffraction (XRD) and (c) microfocus X-ray fluorescence (XRF).

The infrared spectroscopic method is the same as the X-ray diffraction method, except that the infrared band absorptions are used instead of diffraction intensities. As in the X-ray analysis method, the dependence of the spectrum on temperature or on the presence of diluent can be used to determine which bands are due to the crystalline regions, and which to the amorphous. 

The UV-absorption method, with which quantitative determination of DNA in tissue sections can be done, provided the inspiration for the development of x-ray spectrographic methods at the end of the 1940s. The quantitative x-ray analysis methods were developed to provide quantitative elementary analysis on a histochemical and cytochemical scale, that is, quantitative elemental analysis of tissues in situ and at a subcellular level. Engstrom1 formulated how the problem could be attacked in the following way ... 

Many alternative techniques, both qualitative and quantitative, have been investigated either for screening purposes or as primary methods. Such techniques include atomic absorption spectrophotometry, molecular luminescence, electron spin resonance spectrometry, X-ray analysis methods, and electro analytical methods. Flameless atomic absorption spectrophotometry (FAAS) is the technique that has almost completely replaced NAA. 

The investigated samples were stainless steel (12X18H10T) membranes with diameter 40 mm and thickness 0.2 mm. Some part of samples was covered by thin titanium nitride film plotted by vacuum ion-plasma sputtering. The typical thickness of the covering was 10 micrometers. Stehiometry of thin-film coats was explored by x-ray analysis method and turned out to be close to ideal. 

Tian, H.H., and Atzmon, M., Comparison of X-ray analysis methods used to determine the grain size and strain in nanocrystalline materials. Philos. Mag. A, 79 (4), 1769-1786, 1999. 

As one can observe, for a solution with concentrations ranging between 0.035 and 0.35 w/v % range, silver crystals were formed on the cellulose smface whereas, for a solution with a content of 0.0035 w/v % or less, no physical binding was observed between silver and the cellulosic substrate. The observed silver crystals had a hexagonal shape, their size varying between 1 and 10 pm in diameter. Formation of these crystals was analyzed using energy dispersive X-Ray analysis method. Finally, analysis has demonstrated that the chemically bonded ionic silver... 

X-ray analysis methods (including diffraction and reflectometry) described in Chap. 1 are the most widely used tools for the identification of crystalline properties of materials, in addition to materials strain, texture, stress, density, and surface roughness—properties that are key parameters for various industrial applications. Chapter 2 covers a wide range of optical characterization techniques with focus on ellipsometry, Raman scattering, Fourier transform infrared spectroscopy, and spectrophotometry. Those methods, covering a wide range of photon energy and laser... 

A scanning electron microscope can also be equipped with additional instmmentation for electron-excited x-ray analysis (9). In many systems, this is performed in the mode known as energy dispersive x-ray analysis (edx). Other common acronyms for this method are eds for energy dispersive spectroscopy or edax for energy dispersive analysis of x-rays. 

The formation of such materials may be monitored by several techniques. One of the most useful methods is and C-nmr spectroscopy where stable complexes in solution may give rise to characteristic shifts of signals relative to the uncomplexed species (43). Solution nmr spectroscopy has also been used to detect the presence of soHd inclusion compound (after dissolution) and to determine composition (host guest ratio) of the material. Infrared spectroscopy (126) and combustion analysis are further methods to study inclusion formation. For general screening purposes of soHd inclusion stmctures, the x-ray powder diffraction method is suitable (123). However, if detailed stmctures are requited, the single crystal x-ray diffraction method (127) has to be used. 

Chemical conversion of compounds to intermediates of known absolute configuration is a method routinely used to determine absolute configuration (86). This is necessary because x-ray analysis is not always possible suitable crystals are required and deterrnination of the absolute configuration of many crystalline molecules caimot be done because of poor resolution. Such poor resolution is usually a function of either molecular instability or the complex nature of the molecule. For example, the relative configuration of the macroHde immunosuppressant FK-506 (105) (Fig. 8), which contains 14 stereocenters, was determined by x-ray crystallographic studies. However, the absolute configuration could only be elucidated by chemical degradation and isolation of L-pipecoUc acid (110) (80). 

Chemical Properties. Elemental analysis, impurity content, and stoichiometry are determined by chemical or iastmmental analysis. The use of iastmmental analytical methods (qv) is increasing because these ate usually faster, can be automated, and can be used to determine very small concentrations of elements (see Trace AND RESIDUE ANALYSIS). Atomic absorption spectroscopy and x-ray fluorescence methods are the most useful iastmmental techniques ia determining chemical compositions of inorganic pigments. Chemical analysis of principal components is carried out to determine pigment stoichiometry. Analysis of trace elements is important. The presence of undesirable elements, such as heavy metals, even in small amounts, can make the pigment unusable for environmental reasons. 

In this work the results of reseai ch common sorbtion-X-Ray-fluorescence analysis of Pb(II), Cd(II), Zn(II) and Mo(VI) with preconcentration on complexing chemical silica gel modified with mercaptane groups and modified with 8-hydroxyquinoline were described. The conditions and limits of determination of the X-Ray-fluorescence method in the thin lawyers ai e discussion. 

If the sample is an insulator there are still methods by which it can be studied in the instrument. The simplest approach is to coat it with a thin (10-nm) conducting film of carbon, gold, or some other metal. In following this approach, care must be taken to avoid artifacts and distortions that could be produced by nonuniform coatings or by agglomeration of the coating material. If an X-ray analysis is to be... 

In principle all the X-ray emission methods can give chemical state information from small shifts and line shape changes (cf, XPS and AES in Chapter 5). Though done for molecular studies to derive electronic structure information, this type of work is rarely done for materials analysis. The reasons are the instrumental resolution of commercial systems is not adequate and the emission lines routinely used for elemental analysis are often not those most useftil for chemical shift meas-ure-ments. The latter generally involve shallower levels (narrower natural line widths), meaning longer wavelength (softer) X-ray emission. 

Although XRF is generally the X-ray spectrometry method of choice for analysis of major and trace elements in bulk specimens, useful PIXE measurements can be made. A detailed review of the main considerations for thick-target PEXE provides guidance for trace analysis with known and unknown matrices and bulk analysis when the constituents are unknown. Campbell and Cookson also discuss the increased importance of secondary fluorescence and geometrical accuracy for bulk measurements. 

Examination of the structural consequences of these complex interacting factors is now being elucidated in considerable detail by systematic application of electron optical and X-ray analysis techniques, as well as by a range of other methods . 

The Ca-Cu system has been reexamined using thermal analysis and x-ray diffraction methods an independent study of the CaCuj-Cu section has also been completed. The resultant phase diagram, although similar to that in ref. 3 at the Cu-rich end, differs markedly for Ca-rich alloys. Supporting evidence for the modifications has been obtained from the Ca-Mg-Cu ternaiy system. Three intermediate compounds are formed in the system CaCuj (950 C) melts congruently, whereas CajCu (488 C) and CaCu (567°C) are formed in peritectic reactions. Single-crystal x-ray diffraction studies verify the stoichiometry of CajCu and examine the polymorphism of CaCu. ... 

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