Microanalysis

Chemical analysis of a very small region in a large sample is called microanalysis. The diameter of the analyzed region is of the order of a micron or less. Such analysis can be done with an x-ray microprobe (x-ray microanalyzer) or with various forms of the electron microscope, if the latter is equipped with an x-ray spectrometer. 

These devices are collectively known as electron-column instruments. They all may be likened to elaborate x-ray tubes, in which the specimen is the target and in which extreme measures have been taken to focus the electron beam from the filament into a very small spot. 

This instrument always includes an x-ray spectrometer, because its whole purpose is chemical analysis. It came into general use in the early 1950s but is currently being replaced in many laboratories by spectrometer-equipped electron microscopes. 

Both the electron column and the adjacent spectrometer are highly evacuated, a circumstance that improves light element detectability. With a crystal spectrometer all elements down to boron (Z = 5) can be detected. 

In this instrument the primary purpose of the electron beam is to produce an image, and sometimes an electron diffraction pattern, of the sample. However, the electrons hitting the sample also generate x-rays, and a chemical analysis of the electron-irradiated area is therefore possible if a spectrometer is attached to the microscope. 

There are several schools of thought on this topic. Some maintain that all new compounds must be analysed, whereas others say that, with the modem array of physical methods (high resolution nmr spectroscopy and high resolution soft ionization mass spectroscopy, for example) the need for combustion analysis no longer exists. Many follow a middle course and use microanalysis for crystalline compounds which are available in sufficient quantity, and high resolution mass spectrometric measurements in all other cases. The course you take will depend upon circumstances (the requirements of your supervisor or the department, for example). 

Microanalytical data should be within 0.3 - 0.5% of theory. If this is not the case, then the sample is either impure in some way, or not what you think it is. Try to fit the data to a sensible molecular formula, and if a good 

If you cannot obtain a fit with any reasonable molecular formula, then accept that the sample must have been less pure than you thought. Repurify another sample and try again. 

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R. E. Lee, Scanning Electron Microscopy and X-Ray Microanalysis, PTR Prentice Hall, Englewood Cliffs, NJ, 1993. 

We have also added an entirely new section dealing with semi-microanalysis. In our original Introduction (p. ix) we justified the retention of macro-methods of quantitative analysis on the grounds that they formed an excellent introduction to micromethods and also afforded a valuable training in exact manipulation generally. By now, however, the macro-estimation particularly of carbon and hydrogen and of nitrogen has disappeared entirely from most laboratories. On the other hand, the micro-... 

Erdey, L. Gravimetric Analysis, Pergamon Oxford, 1965. Steymark, A. Quantitative Organic Microanalysis, The Blakiston Go. New York, 1951. 

L. E. Murr, Electron and Ion Microscopy and Microanalysis Principles and Applications, 2nd ed.. Optical Engineering Vol. 29, Dekker, New York, 1991. 

K. F. J. Heinrich, Electron Beam Microanalysis, Van Nostrand, New York, 1981. 

METHODICAL TECHNIQUES FOR RESEARCH OF RARE-METAL AND RARE-EARTH MINERALS WITH X-RAY MICROANALYSIS... 

The X-ray microanalysis is the basic method of study of rare-metal and rare-earth minerals of micron size. The multi-component composition, instability of minerals under the electron beam, overlap of X-ray characteristic lines, absence of reference samples of adequate composition present difficulties in the research of mineral composition. 

The elemental composition of the fish otoliths is a potential source of the useful information to recreate environment history of the individual fish in some of the species. In-depth study of the chemical composition of the otolith center (formed eaidy in fish life) and otolith edge (formed later in fish life) ensures chronological and environmental information stored in the otoliths [1]. This infoiTnation may be achieved by X-ray electron probe microanalysis (EPMA). EPMA is the analytical method to determine the elemental composition of different otolith s parts, their sizes varying from ten up to some tens of microns. 

Elemental organic microanalysis is one of the main methods for purity verification of organic and organoelement compounds and polymers. 

The complex of the following destmctive and nondestmctive analytical methods was used for studying the composition of sponges inductively coupled plasma mass-spectrometry (ICP-MS), X-ray fluorescence (XRF), electron probe microanalysis (EPMA), and atomic absorption spectrometry (AAS). Techniques of sample preparation were developed for each method and their metrological characteristics were defined. Relative standard deviations for all the elements did not exceed 0.25 within detection limit. The accuracy of techniques elaborated was checked with the method of additions and control methods of analysis. 

INVESTIGATION OF INDIVIDUAL PARTICLES OF ZEOLITE POWDER BY X-RAY ELECTRON PROBE MICROANALYSIS... 

The powders of zeolites of various trademarks are used to produce petroleum-refining catalysts. In this connection, it is very important to have complete information concerning not only chemical composition and distribution of impurity elements, but also shape, surface, stmcture and sizes of particles. It allows a more detailed analysis of the physical-chemical characteristics of catalysts, affecting their activity at different stages of technological process. One prospective for solving these tasks is X-ray microanalysis with an electron probe (EPMA). 

Survey capability with ppm detection limits, not affected by surface charging effects complete elemental coverage survey microanalysis of contaminated areas, chemical failure analysis... 

J. I. Goldstein, Dale E. Newbury, P. Echlin, D. C. Joy, C. Fiori, and E. Lif-shin. Scanning Microscopy and X-Ray Microanalysis. Plenum Press, New York, 1981. An excellent and widely ranging introductory textbook on scanning microscopy and related techniques. Some biological applications are also discussed. 

L. Reimer. Transmission Electron Microscopy Physics of Image Formation and Microanalysis. Springer-Verlag, Berlin, 1984. This is an advanced but comprehensive source on TEM. Reimer also authored a companion volume on SEM. 

Electron Probe Microanalysis, EPMA, as performed in an electron microprobe combines EDS and WDX to give quantitative compositional analysis in the reflection mode from solid surfaces together with the morphological imaging of SEM. The spatial resolution is restricted by the interaction volume below the surface, varying from about 0.2 pm to 5 pm. Flat samples are needed for the best quantitative accuracy. Compositional mapping over a 100 x 100 micron area can be done in 15 minutes for major components Z> 11), several hours for minor components, and about 10 hours for trace elements. 

Quantitative Electron-Probe Microanalysis. (V. D. Scott and G. Love, eds.) John Wiley Sons, New York, 1983. Taken from a short course on the electron microprobe for scientists working in the field. A thorough discussion of EDS and WDS is given, including experimental conditions and specimen requirements. The ZAF correction factors are treated extensively, and statistics, computer programs and Monte Carlo methods are explained in detail. Generally, a very useftd book. 

The STEM is unrivaled in its ability to obtain high-resolution imaging combined with microanalysis from specimens that can be fashioned from almost any solid. Major applications include the analysis of metals, ceramics, electronic devices... 

The major STEM analysis modes are the imaging, diffraction, and microanalysis modes described above. Indeed, this instrument may be considered a miniature analytical chemistry laboratory inside an electron microscope. Specimens of unknown crystal structure and composition usually require a combination of two or more analysis modes for complete identification. 

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