Energy Dispersive Electron Probe Microanalysis Research Articles

Feasibility of combined wavelength/energy-dispersive computer-controlled scanning electron microscopy for determining trace metal distribution

The utility of wavelength-dispersive and energy-dispersive electron probe microanalysis (WD-ED EPMA) for quantifying the distribution of seven trace metals (Cr, Ni, As, Se, Cd, Hg, and Pb) among coal minerals and ash particles was investigated. The technique is limited to analyzing particles greater than about 7 μm in diameter because of the relatively intense beam conditions (25 kV, 100 nA) required to attain reasonable detection sensitivity; statistical limits of detection are generally < 300 ppm for a WD spectrometer (xenon-filled detector) and 100 s counting time. The application of WD EPMA to a glass standard, compositionally analogous to coal ash, indicates that Cr, Ni, As, and Cd can be determined routinely at concentrations ranging from about 200–500 ppm with reasonable accuracy and precision. Lead, with a consensus value of 418 ppm, was detected in the glass, but could not be quantified accurately with the general analysis conditions employed. The metals Ni and Se were detected and quantified in pyrite during a cursory application of automated WD-ED EPMA to minerals in the Illinois No. 6 and Pittsburgh No. 8 Argonne premium coals. WD-ED EPMA and computer-controlled scanning electron microscopy can be combined to determine trace metal distribution among the inorganic constituents of coal and ash as a function of particle size.

Interface abruptness in LPE grown (CdHg) Te layers on CdTe substrates

The abruptness of interfaces between liquid phase epitaxial grown layers of Cd x Hg 1 - x Te and the CdTe(111) substrates on which they are grown has been studied by four techniques used for compositional profiling. These are: (i) energy-dispersive electron probe micro-analysis (ED-EPMA) at 5 and 25 kV; (ii) wavelenght-dispersive electron probe micro-analysis (WD-EPMA) at 15 kV; (iii) secondary-ion mass spectrometry SIMS) using a 12.5 kV O + 2 primary beam and (iv) backscattered electron analysis analysis (BSE) in the scanning electron microscope at 15 and 35 kV. These techniques have been applied to specimens from a single epitaxial layer. The distances as for the 10% to 90% compositional transition were measured, and values varying from 2 mum for ED-EPMA to 0.23 mum for BSE analysis were found. These results indicate the misleading measurements of interface abruptness that can be obtained on epitaxial specimens if consideration is not paid to the spatial resolution of the measurement technique and the topographic structure of the specimen. The potential of the BSE technique for high resolution compositional profiling and two-dimensional mapping will be discussed and the causes of the erroneous results obtained with the other techniques will be highlighted. The fact that the interface abruptness in this LPE specimen (≤ 0.23 mum) is a factor of ten less than conventionally measured for LPE (CdHg)Te layers has important consequences for the use of LPE for the growth of multilayer IR detector structures.

Electron probe microanalysis of thin films at variable angle of incidence

Thin films of NiCrSi with thicknesses ranging from 3 to 80 nm were irradiated by 15 keV electrons. The angle of incidence was varied between normal and nearly grazing incidence by tilting the sample up to β=85°. At oblique incidence the detection limits of energy dispersive electron probe microanalysis for surface layers are higher by at least one order of magnitude than at normal incidence. Less than 1/10 of a monolayer is detectable. Furthermore, one gets informations concerning the depth distribution of the constituents. For example, less than 3 monolayers of Cu were detected and localized under a 9 nm thick NiCrSi film on vitreous carbon.

SEM and elemental analysis of composite resins

Twenty-four chemically cured, 21 light-cured anterior, three light-cured anterior/ posterior, and 18 light-cured posterior composite resins were examined using scanning electron microscopy, and the elemental composition of their filler particles was analyzed with an energy dispersive electron probe microanalyzer. According to the results obtained, the composite resins were divided into five groups (traditional, microfilled type, submicrofilled type, hybrid type, and semihybrid), with two additional hypothetical categories (microfilled and hybrid). Characteristics of each type were described with clinical indications for selective guidance of respective composite resins for clinical use.

Ion Beam Analysis of Pigments

AbstractWe have analyzed single and multiple layer paint samples to evaluate 3 MeV external beam proton induced X-ray emission (PIXE) for elemental analysis of inorganic pigments. The results are compared to those from energy dispersive electron microprobe analysis and Rutherford Backscattering Spectrometry (RBS). The advantage of PIXE is that the protons' penetration depth of 100 microns is more than 25 times greater than that of 20 keV electrons and 10 times greater than 3 MeV alpha particles, thus allowing analysis of relatively thick samples of up to 100 microns. The proton beam is passed into the atmosphere (external to the vacuum system) through a thin polymer film, and the beam area on target is 1 mmz. Electron microprobe and RBS require vacuum compatible samples; therefore, the pigments were painted on silicon wafers. Calibration was obtained from metallic thin-film samples of known thickness. The cross calibration of the three analytical techniques allowed evaluation of external PIXE analysis of paint films. We suggest that this nondestructive method is suitable for elemental analysis of drawings and paintings provided that further studies indicate no long term damage is caused.

Detection of cationic and non-cationic markers in the rat glomerulus by electron probe analysis

Acidic glycans (glomerular polyanion substances) in the rat kidney were visualized ultrastructurally by three cationic markers: colloidal iron, ruthenium red, and polyethylenimine-phosphotungstic acid (PEI-PTA). Heavy metal atoms (Fe, Ru and W) were detected in ultrathin sections by energy-dispersive electron probe microanalysis (EPMA). Characteristic peaks of the locally bound elements were obtained in spectra derived from the dense structures seen by transmission electron microscopy (TEM)--i.e. the glycocalyx of podocytes and/or the polyanion sites in the lamina rara externa of the glomerular basement membrane. Weaker signals were emitted by some extraglomerular structures. This finding may reflect a low concentration of glycans in structures lacking apparent density by TEM, and/or incomplete specificity of the markers, partial dislocation of reactive substances or the presence of an endogenous element (Fe). Experimental argyrosis was elicited by the peroral administration of silver nitrate. Dense Ag precipitates were seen chiefly in the lamina densa and characteristic peaks of silver were displayed in this site by EPMA, and was best demonstrated in non-contrasted sections. A single i.v. injection of Ag proteinate failed to produce glomerular pigmentation. The only dense granular product in tubular cells yielded characteristic peaks of Fe (endogenous siderosomes) but EPMA excluded detectable amounts of silver.

The mechanism of acute cytotoxicity of triethylphosphine gold(I) complexes: I. Characterization of triethylphosphine gold chloride-induced biochemical and morphological changes in isolated hepatocytes

Triethylphosphine gold complexes are effective therapeutic agents used for the treatment of rheumatoid arthritis. Many of those molecules are also highly cytotoxic in vitro and can inhibit DNA and protein synthesis. Preliminary experiments have indicated that triethylphosphine gold chloride (TEPAu) may induce the peroxidative decomposition of cellular membrane lipids. The purpose of these investigations therefore was to evaluate the role of lipid peroxidation in the mechanism of acute cytotoxicity of a gold(I) coordination complex, TEPAu, and to examine the early morphological and biochemical changes induced by TEPAu in suspensions of freshly isolated rat hepatocytes. TEPAu caused a rapid loss of cell viability at concentrations above 25 μ m which was significantly different from that of control by 60 min and complete by 180 min of incubation. TEPAu also depleted cells of reduced glutathione (GSH) and increased the formation of malondialdehyde (MDA) by 60 min. Incubation of cells with either of the antioxidants, N,N′-diphenyl- p-phenylenediamine (DPPD) or promethazine blocked the formation of MDA but did not alter the time course of cell death or GSH depletion induced by TEPAu. TEPAu also caused a decrease in cellular NADPH and NADH by 10 min. Electron microscopy of hepatocytes exposed to TEPAu revealed early (5 min) formation of flocculent electron-dense precipitates within condensed mitochondria. These changes characteristically preceded cell death. Energy-dispersive electron-probe microanalysis indicated that the electron-dense precipitates did not contain detectable amounts of gold. TEPAu also caused a concentration-dependent decrease in cellular ATP and oxygen consumption in isolated rat hepatocytes. These data suggest that lipid peroxidation, as indicated by the formation of MDA, is probably not a major mechanism by which triethylphosphine gold complexes lethally injure cells. These data, therefore, suggest that mitochondria may be target organelles in TEPAu-induced toxicity to isolated rat hepatocytes.

Postdepositional modification of uraninite-bearing quartz-pebble conglomerates from the Quirke ore zone, Elliot Lake, Ontario

Petrographic observations, backscattered electron imagery (spatial resolution = + or -0.1 mu m), and semiquantitative energy dispersive electron microprobe analysis indicate that postdepositional modification of the uraniferous conglomerates occurred in three stages. The first involved complete fluid-mediated leaching of Fe from detrital ilmeno-magnetite grains and mobility of U, Th, rare earth elements, Y, PO 4 (super -2) , and SiO 2 . Uraninite was replaced by coffinite ([U, Th]SiO 4 ) and quartz, detrital monazite was dissolved and slightly altered to urano-thorite ([Th, U]SiO 4 ), U reacted with TiO 2 derived from detrital grains to form composite grain aggregates composed of brannerite ( approximately UTi 2 O 6 ) and other alteration products, and coffinite together with a Y-rare earth elements-U phosphate precipitated in the matrix. The next stages involved the precipitation of the secondary pyrite and the occlusion of the conglomerate pore space by secondary quartz and sericite. The most probable Eh-pH fields for the ground waters involved in postdepositional modification are low to moderate Eh and slightly acid pH for ilmeno-magnetite leaching, and low Eh and near-neutral pH for pyrite precipitation. Both inferred Eh-pH fields fall within the thermodynamic stability fields of uraninite and coffinite in which uranium solubilities are low. Phosphate dissolved from monazite and apatite could have enhanced uranium solubility at the higher inferred Eh values. Conclusion that neither the deposition nor the preservation of detrital uraninite can logically be used to draw conclusions about the oxygen content of the Precambrian atmosphere at approximately 2,350 m.y. ago.--Modified journal abstract.

Intracellular electrolyte concentrations in rat sympathetic neurones measured with an electron microprobe.

Intracellular element concentrations were measured in rat sympathetic neurones using energy dispersive electron microprobe analysis. The resting intracellular concentrations of sodium potassium and chloride measured in ganglia maintained for about 90 min in vitro at 25 degrees C were 3, 155 and 25 mmol/kg total tissue wet weight respectively. Recalculated in mmol/l cell water, these values are 5, 196 and 32 respectively. There were no significant differences between the nuclear and cytoplasmic values of these ions. Incubation in either carbachol (180 mumol/l, 4 min) or ouabain (1 mmol/1, 60 min) significantly increased the intracellular sodium and decreased the intracellular potassium concentrations. Neither substance materially altered the intracellular chloride concentration. The data obtained are compared and contrasted to those obtained in mammalian sympathetic neurones using chemical analysis and ion-sensitive microelectrodes.

An electron microprobe study of some Alberta placer gold

The detailed characteristics of 435 placer gold grains from the North Saskatchewan and Athabasca rivers have been investigated using a combination of optical microscopy, energy dispersive electron microprobe analysis and SEM techniques. Most grains show high-fineness rims surrounding lower-fineness cores (giving an extreme range of 4.3%–46.1% Ag within an individual grain). Characteristics of the rims lend support to the hypothesis that they are the products ofin situ leaching of silver followed by transport which largely destroys a spongy texture produced by the leaching. There is no change in the average Ag content of grains of any given size range with distance downstream, which also indicates that all significant leaching takes place before transportation. However, differences are apparent in the average Ag content with grain size.

Intracellular analysis of sodium, potassium, and chloride in mouse erythrocytes

Recently, Cameron et al. ('79) published measurements of intracellular solute amounts (expressed as mmoles per kilogram dry cell solids) obtained by energy dispersive electron probe microanalysis in different rodent tissues. In this communication, I wish to compare Cameron et al.'s ('79) erythrocyte values of Na, K, and Cl with those I have made using more conventional techniques of elemental analysis. This comparison is necessitated by Cameron et al.'s ('79) observation of extremely high intracellular sodium levels. If their findings are accurate, the possibility of a polymorphism with respect to intracellular Na levels therefore presents itself. If a polymorphism between different inbred strains of mice exists, and if, as in ruminants, this trait has a genetic basis, an examination of the genetic aspects of the control, differentiation, and the ultimate expression of the ion transport mechanisms responsible would undoubtedly provide insight into the molecular basis as well as the adaptive dynamics of transport systems in general.

The atomic number dependence of the X‐ray continuum intensity and the practical calculation of background in energy dispersive electron microprobe analysis

AbstractComputer fitting techniques have been used to derive a new expression for the relationship between X‐ray continuum intensity and atomic number for a range of electron acelerating potentials up to 25 kV, continuum energies up to 10 keV and average atomic numbers up to thirty. A practical approach to background corrections in energy dispersive electron microprobe analysis, which utilizes this expression, is outlined. The procedure should lead to significant improvements in both accuracy and detection limits in this method of X‐ray analysis.

A direct fusion method of preparing silicate rock glasses for energy-dispersive electron microprobe analysis

A method of preparation of homogeneous glass beads by direct fusion of bulk rock powders on an iridium-strip heater, and the quantitative analysis of these glasses using an electron microprobe fitted with an Si(Li) detector, are described. Major element concentrations obtained for international geochemical reference standards are of high precision, and agree well with recommended values obtained by other methods.