Scanning elemental analyses

Multielemental Analysis Atomic emission spectroscopy is ideally suited for multi-elemental analysis because all analytes in a sample are excited simultaneously. A scanning monochromator can be programmed to move rapidly to an analyte s desired wavelength, pausing to record its emission intensity before moving to the next analyte s wavelength. Proceeding in this fashion, it is possible to analyze three or four analytes per minute. 

The electron-optical performance of the EPMA system is indistinguishable from that of a conventional scanning electron microscope (SEM) thus, EPMA combines all of the imaging capabilities of a SEM with quantitative elemental analysis using both energy- and wavelength-dispersive X-ray spectrometry. ... 

ADMET polymers are easily characterized using common analysis techniques, including nuclear magnetic resonance ( H and 13C NMR), infrared (IR) spectra, elemental analysis, gel permeation chromatography (GPC), vapor pressure osmometry (VPO), membrane osmometry (MO), thermal gravimetric analysis (TGA), and differential scanning calorimetry (DSC). The preparation of poly(l-octenylene) (10) via the metathesis of 1,9-decadiene (9) is an excellent model polymerization to study ADMET, since the monomer is readily available and the polymer is well known.21 The NMR characterization data (Fig. 8.9) for the hydrogenated versions of poly(l-octenylene) illustrate the clean and selective nature of ADMET. 

The scanning transmission electron microscope (STEM) was used to directly observe nm size crystallites of supported platinum, palladium and first row transition metals. The objective of these studies was to determine the uniformity of size and mass of these crystallites and when feasible structural features. STEM analysis and temperature programmed desorption (TPD) of hydrogen Indicate that the 2 nm platinum crystallites supported on alumina are uniform In size and mass while platinum crystallites 3 to 4 nm in size vary by a factor of three-fold In mass. Analysis by STEM of platinum-palladium dn alumina established the segregation of platinum and palladium for the majority of crystallites analyzed even after exposure to elevated temperatures. Direct observation of nickel, cobalt, or iron crystallites on alumina was very difficult, however, the use of direct elemental analysis of 4-6 nm areas and real time Imaging capabilities of up to 20 Mx enabled direct analyses of these transition metals to be made. Additional analyses by TPD of hydrogen and photoacoustic spectroscopy (PAS) were made to support the STEM observations. 

Electrolysis of a solution of the catalyst at — 1.4 V to — 1.5 V vs. SCE in the absence of C02, giving le /Re atom, gave the sparingly soluble green dimer (as characterised by UV-visible, [R, nmr and elemental analysis on the isolated material) in agreement with the work of Lehn and colleagues (Hawecker, 1983) and showing that the first reduction is coupled to the formation of the dimer if chloride loss is allowed to occur. If the cyclic voltammetric scan was reversed when the potential reached —1.5 V, at a... 

Electron probe microanalysis functions by direct examination of the primary X-rays produced when the specimen is used as a target for an electron beam. Focused electron beams allow a spot analysis of a 1 pm3 section of the specimen. One current development employs the electron beam within a scanning electron microscope to provide both a visual picture of the surface of the sample and an elemental analysis of the section being viewed. Spectra obtained from primary X-rays always have the characteristic emission peaks superimposed on a continuum of background radiation (Figure 8.32). This feature limits the precision, sensitivity and resolution of electron probe microanalysis. 

Carr, R. G. (1988). Finite element analysis of PZT tube scanner for scanning tunneling microscopy. /. Microscopy 152, Part 2, 379-385. 

Other desirable features of a monochromator are stability and multi-element capabUity. Initially, direct reading spectrometers, based on a polychromator, were used for simultaneous multi-element analysis, although these were expensive, bulky and generally limited to specific elements. The development of rapid-scanning monochromators under... 

One of the more recent branches of atomic spectrometry, although perhaps the most exciting one, is atomic mass spectrometry, which has had a very important impact on science and technology. At present, atomic mass spectrometry is ordinarily performed using inductively coupled plasma ion sources and either a quadrupole or a scanning sector-field mass spectrometer as an analyser. The remarkable attributes of such a combination, being an indispensable tool for elemental analysis, include ... 

Current methods used to image MCM-41 include (1) analytical transmission electron microscopy (TEM) to determine structure, size, morphology, and local chemical composition (2) energy-dispersive X-ray spectroscopy (EDXS) in a scanning electron microscope (SEM) to determine chemical composition 5 and (3) electron energy loss spectroscopy (EELS) for elemental analysis.6... 

Forslind, B. etal., Elemental analysis on freeze dried sections of human skin studies by electron microprobe and particle induced x-ray emission analysis, Scanning Electron Microsc., 2, 755, 1984. 

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