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Results for “Electron Probe Microanalysis”

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PubMed1983

The role of molybdenum in human biology.

Molybdenum, because of its unique chemistry, is the biological catalyst for reactions in which proton and electron transfer, and possibly oxygen transfer, are coupled. The molybdoenzymes in man are sulphite oxidase, xanthine oxidase/dehydrogenase and aldehyde oxidase. The former is essential for detoxication of the sulphite arising from metabolism of sulphur-containing amino acids, from ingestion of bisulphite preservative and from inhalation of sulphur dioxide, an atmospheric pollutant. Whether, or not, any of the reactions catalysed by xanthine oxidase/dehydrogenase and aldehyde oxidase are necessary for human well-being has yet to be established.

Chemical Phenomena↗
PubMed1978

Lead-loaded ion-exchange resin bead as a calcergen.

Several heavy metals have direct calcifying effects in connective tissues; most notable among them is lead (Pb), whether administered topically (1) or systemically with local injury (2). The mechanisms of metal-induced soft tissue calcification have been studied by injecting salts of known in vitro calcifying potential into subcutaneous connective tissue (3); of the metals used, only lead and holmium produced an early accumulation of minerals on collagen in vivo. Lead is also claimed to accelerate bone healing in the rabbit leg with no toxic effects (4). Lead-loaded ion-exchange resin beads, implanted into surgically prepared subcutaneous pouches in rats, rapidly induced subcutaneous calcification which has been studied by microradiography and electron-probe microanalysis.

Animals↗
PubMed1986

Detection and localization of silicon and associated elements in vertebrate bone tissue by imaging ion microscopy.

The growing long bones from normal embryonic chicks and young rats have been examined in situ by imaging ion microscopy, a highly sensitive technique for elemental detection and localization. In tibial diaphyses from chick and rat, treated with anhydrous ethylene glycol, embedded in Spurr medium, and dry sectioned 1-2 microns thick, analyses revealed the presence of silicon, calcium, magnesium, carbon, and oxygen. Silicon localization was principally extracellular in the tissues. Comparison of single element maps of silicon and calcium indicated that silicon specifically appeared in putative uncalcified osteoid regions of tibiae. Detection and imaging of silicon by ion microscopy support results of earlier work by Carlisle, who demonstrated the element in osteoid of rat and mouse bone by electron probe microanalysis. The current data offer the possibility for characterizing more completely silicon interaction in vertebrate calcified tissues.

Animals↗
PubMed2005

Analytical evidence of amorphous microdomains within nitridosilicate and nitridoaluminosilicate single crystals.

Single crystals of new nitridosilicates and nitridoaluminosilicates with excellent R values in X-ray investigations were analysed quantitatively using 30 to 60 microm single-spot LA-ICP-MS. Significant discrepancies between expected and measured chemical composition could not be explained by the crystallographic data. High spatial resolution analysis using electron probe microanalysis (EPMA, 10 microm) leads to the discovery of inhomogeneities in the crystalline material. The application of standard single-spot LA-ICP-MS with a spatial resolution of 30 to 60 microm is not suitable for the analysis of these crystals as the existing inhomogeneities dominate and alter the determined concentrations. However, owing to the better detection capabilities, a scanning LA-ICP-MS procedure enables a more representative analysis of single crystals of Ca(5)Si(2)Al(2)N(8) than single-spot LA-ICP-MS as a result of a larger sampling volume. It is highly likely that these impurities consist of amorphous, vitreous phases as powder diffraction X-ray data indicates the existence of a significant fraction of an X-ray amorphous material besides crystalline silicates. These microdomains contain less aluminium, silicon and calcium or are nearly free of aluminium, which explains the detected discrepancies in the chemical composition.

Journal Article↗
PubMed2000

Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) for spatially resolved trace analysis of early-medieval archaeological iron finds.

The suitability of laser ablation ICP-MS for minor and trace analysis of archaeological iron finds, produced by a direct reduction process in a 'bloomery' furnace, is reported. The analysis of elemental impurities in the iron can provide useful archaeometallurgical information on the production process and the provenance of the iron. Since, even after refinement, the iron resulting from this process may contain many inclusions (slag, charcoal, holes, etc.), a method should be used with sufficient spatial resolution to preclude the inclusions from the analysis. The ablation parameters are selected such that ablation craters of approx. 100 microm in diameter are obtained. The method is validated with low alloy steel and cast iron standard reference materials and by a comparative analysis with electron probe microanalysis (EPMA). The precision is limited mainly by the homogeneity of the iron, rather than by instrumental reproducibility. The advantages and drawbacks of the method are briefly compared with EPMA. Preliminary results from the analysis of archaeological iron samples from excavations at Develier-Courtetelle (Canton Jura, CH), Neftenbach (Canton Zurich, CH), Wartau (Canton St Gallen, CH) and Mont Chemin (Canton Valais, CH) are given.

Journal Article↗
PubMed2001

Topochemical investigation of ancient manuscripts.

Various modern instrumental techniques for surface analysis were applied for the non-destructive physicochemical examination of works of art. As samples, pieces of ancient manuscripts endangered by iron-gall ink corrosion were used. Surface characterisation of the morphology of the cellulose fibres within corroded and non-corroded parts of the manuscript performed by scanning electron microscopy (SEM) showed seriously damaged cellulose fibres in the written parts. The elemental composition of selected parts of the manuscript was determined by energy dispersive X-ray fluorescence analysis (EDX). A more detailed study of the paper surface was then performed by electron probe microanalysis (EPMA). This technique yields the morphological characteristics of the surface as well as element distribution maps over the written area of the investigated manuscript.

Journal Article↗
PubMed2001

Quantification of corrosion phenomena in plastic processing machines.

In a model platelet system the corrosion of metallic materials was studied by processing polyethylene, polyphenylene sulfide, and glass-fibre-reinforced polyphenylene sulfide. The measurement methods used were scanning electron microscopy (images), electron-probe microanalysis (lateral element maps), secondary-ion mass spectrometry (depth profiles), X-ray photoelectron spectroscopy (chemical bonding), and grazing-incidence X-ray diffraction (structures of crystalline compounds). As nondestructive measure of corrosive attack, grazing-incidence X-ray diffraction, using the intensity ratio (IFe-O/IFe), was found to be the method of choice. The reproducibility for the total procedure was found to range between 6 and 13% (rel.). The intensity ratio was examined as function of depth, of the time of stress, of material composition, and of the surrounding atmosphere. Oxides were identified as main corrosion products. The extent of oxide formation is proportional to the time elapsed after processing.

Journal Article↗
PubMed1996

Fluoride analysis of apatite crystals with a central planar OCP inclusion: concerning the role of F- ions on apatite/OCP/apatite structure formation.

To study the roles of F- ions in the formation of apatite crystals embedding octacalcium phosphate (OCP) lamella in the center of apatite (Ap), a range of the Ap/OCP/Ap lamellar-mixed crystals were synthesized under various concentrations of fluoride ion (F-) from 0. 1-1.0 ppm at pH 6.5 and 37 degrees C. The products were analyzed for the F- incorporation, F- distribution, and the amount of OCP and Ap by chemical analysis, X-ray diffraction (XRD), electron probe microanalysis (EPMA), and nuclear magnetic resonance (NMR) techniques. The F- content and the amount of apatite in the crystalline product increased with an increase in the F- concentration in solution, whereas the amount of OCP and the yield of total product decreased. EPMA indicated that F- ions are distributed in the crystals almost homogeneously. The combined analysis suggested that a low-substituted fluoridated hydroxyapatite (FHAp) grew on a small amount of F--containing OCP or on a surface-reaction layer of OCP, which has accumulated a small amount of F-. The roles of F- ions were hypothesized as the reduction of the growth rate and/or the critical thickness in the a*-axis direction of OCP, the enhancement of hydrolysis of OCP, and the activation of the growth of FHAp, resulting in thinner OCP lamella and thicker apatite lamella in the a*-axis direction with an increase in F- concentration.

Apatites↗
PubMed2000

H+-and K+-dependence of Ca2+ uptake in lung lamellar bodies.

Lung lamellar bodies maintain an acidic interior by an energy-dependent process. The acidic pH may affect the packaging of surfactant phospholipids, processing of surfactant proteins, or surfactant protein A-dependent lipid aggregation. The electron-probe microanalysis of lamellar body elemental composition has previously suggested that lamellar bodies contain high levels of calcium some of which may be in ionic form. In this study, we investigated the Ca2+ uptake characteristics in isolated lung lamellar bodies. The uptake of Ca2+ was measured by monitoring changes in the fluorescence of Fluo-3, a Ca2+ indicator dye. The uptake of Ca2+ in lamellar bodies was ATP-dependent and increased with increasing concentrations of Ca2+. At 100 nM Ca2+, the uptake was almost completely inhibited by bafilomycin A1, a selective inhibitor of vacuolar type H+-ATPase, or by NH4Cl, which raises the lamellar body pH, suggesting that the pH gradient regulates the uptake. The uptake of Ca2+ increased as the Ca2+ concentration was increased, but the relative contribution of bafilomycin A1-sensitive uptake decreased. At 700 nM, it comprised only 20% of the total uptake. These results suggest the presence of additional mechanism(s) for uptake at higher Ca2+ concentrations. At 700 nm Ca2+, the rate and extent of uptake were lower in the absence of K+ than in the presence of K+. The inhibitors of Ca2+-activated K+-channels, tetraethylammonium, Penitrem A, and 4-aminopyridine, also inhibited the K+-dependent Ca2+ uptake at 700 nM Ca2+. Thus the uptake of Ca2+ in isolated lung lamellar bodies appears to be regulated by two mechanisms, (i) the H+-gradient and (ii) the K+ transport across the lamellar body membrane. We speculate that lamellar bodies accumulate Ca2+ and contribute to regulation of cytosolic Ca2+ in type II cells under resting and stimulated conditions.

4-Aminopyridine↗
PubMed2001

Extracellular Adenosine Triphosphate Triggers Arrhythmias and Elemental Redistribution in Electrically Stimulated Rat Cardiac Myocytes.

An increase in extracellular adenosine triphosphate (ATP) is arrhythmogenic in rat cardiac myocytes and extracellular ATP levels are elevated during cardiac ischemia. To gain insight into the mechanism by which the arrhythmic contractions are generated, we investigated changes in subcellular elemental content by electron probe microanalysis (EPMA) in isolated adult rat cardiac myocytes stimulated by the ATP analog, 2-methylthio-ATP (2-M-S-ATP). We also measured the effects of 2-M-S-ATP stimulation on myocyte cell shortening. In electrically stimulated myocytes, 2-M-S-ATP stimulation generated arrhythmic contractions and also increased the amplitude of cell shortening. However, only the arrhythmic contractions were reversed by 2-M-S-ATP washout. EPMA of freeze-dried cryosections of rapidly frozen 2-M-S-ATP-stimulated myocytes showed increased cytosolic Na and Cl, decreased K, but no significant change in mitochondrial Ca upon 2-M-S-ATP stimulation. The arrhythmias were abolished upon 2-M-S-ATP washout, and the observed changes in cytosolic elemental content also reversed upon agonist washout, thus suggesting that the increased Na and Cl, and decreased K, are specifically associated with the ATP-dependent spontaneous contractile activity. The observed increase in intracellular Na upon 2-M-S-ATP stimulation may explain our observation of prolonged relaxation time of 2-M-S-ATP-stimulated contractions. This may be due to inhibition of Ca(2+) efflux via the Na(+) Ca(2+) exchanger.

Journal Article↗
PubMed1991

The effect of lead acetate on dentine formation in the rat.

The intravenous injection of lead acetate produces a response in dentine by formation of the so-called lead line. This is associated with a rapid but temporary rise in serum calcium and phosphorus. Previous studies have suggested that lead replaces calcium and phosphorus in the apatite lattice. In this study the lead line was investigated in the scanning electron microscope using backscattered electron imaging and was shown to consist of continuous hypomineralized interglobular spaces within the dentine. Dentine formation was disrupted for at least a week after injection of lead ions. With energy dispersive analysis by X-rays, no localized concentration of lead was detectable within the 'lead line'. It is suggested that the lead line results from a direct effect of lead on the odontoblasts and other hard tissue-forming cells producing a rapid loss of intracellular calcium temporarily displaced by lead ions and a subsequent disturbance of local calcium metabolism.

Animals↗
PubMed1992

Effects of serotonin and carbachol on glial and neuronal rubidium uptake in leech CNS.

Effects of serotonin (5-HT) and carbachol on Rb uptake (used as a K marker) in leech neuron and glia were studied by electron probe microanalysis (EPMA). Hirudo medicinalis ganglia were perfused 60 s in 4 mM Rb substituted normal leech Ringer's with and without 5-HT (dosage range 5-500 microM) or carbachol (range 10-1000 microM), quench frozen cryosectioned, and subjected to EPMA to determine elemental mass fractions and cell water content. Both 5-HT and carbachol altered leech neuron and glial cell elemental distribution and water content. In glial cells, a dose-dependent increase in Rb uptake was observed following 5-HT (control: 26 +/- 2 microM; 5 microM: 47 +/- 4; 50 microM: 62 +/- 4; 500 microM: 82 +/- 11 mmol/kg dry wt. +/- S.E.M.) and carbachol (10 microM: 35 +/- 3; 100 microM: 52 +/- 3; 1000 microM: 68 +/- 3 mmol/kg dry wt. +/- S.E.M.). In neurons, 5-HT and carbachol had small effects. 5-HT decreased glial and neuronal cell water content. Carbachol decreased neuronal (but not glial) water content by approximately the same amount (mean decrease 9%) regardless of dose. Both 5-HT and carbachol affected glial cell K-accumulating properties, providing evidence that certain neurotransmitters may modulate invertebrate glial cells' K clearance function.

Animals↗
PubMed1988

The metal site of stellacyanin: EXAFS studies of the Cu(II), Cu(I), Ni(II) and Co(II) derivatives.

Extended X-ray absorption fine structure (EXAFS) studies of Cu(II) (oxidized), Cu(I) (reduced), Ni(II) and Co(II) stellacyanin from Rhus vernicifera are reported. For Cu(II) stellacyanin, the coordination by three close ligands, viz. 2 N and 1 S, with the presence of smaller shells pointing to imidazole coordination, indicates similarities with the coordination in other so-called type 1 or 'blue'-copper proteins. Upon reduction, slightly longer ligand distances and an additional sulphur ligand are found. Ni(II) and Co(II) stellacyanin resemble Cu(I) and Cu(II) stellacyanin, respectively, in ligand distances, but have a tendency for three rather than two N (or O) ligands in the first shell. The results are compared with the three-dimensional model derived from 1H-NMR relaxation measurements for Co(II) stellacyanin, and are consistent with the proposal that apart from the three close ligands found in all blue-copper proteins, a sulphur from a disulphide bridge and the amide oxygen from an asparagine residue come to within coordinating distance of the metal in stellacyanin.

Binding Sites↗