Automated analysis of SEM X-ray spectral images: a powerful new microanalysis tool.

Spectral imaging in the scanning electron microscope (SEM) equipped with an energy-dispersive X-ray (EDX) analyzer has the potential to be a powerful tool for chemical phase identification, but the large data sets have, in the past, proved too large to efficiently analyze. In the present work, we describe the application of a new automated, unbiased, multivariate statistical analysis technique to very large X-ray spectral image data sets. The method, based in part on principal components analysis, returns physically accurate (all positive) component spectra and images in a few minutes on a standard personal computer. The efficacy of the technique for microanalysis is illustrated by the analysis of complex multi-phase materials, particulates, a diffusion couple, and a single-pixel-detection problem.

Electron ionization cross sections for atomic subshells.

Ionization of atoms is the first step in many analytical procedures. The cross section for ionizing a particular atomic shell is essential for calculating the magnitude of analytical signals. Calculations using atomic wave functions for various shells of all elements relevant for X-ray microanalysis over a range of electron energies up to 400 keV were performed. The calculations for high energies above threshold can be considerably simplified by using the mathematical form of the Bethe ridge that dominates the scattering in this region. Corrections for exchange at low energies above threshold are incorporated in these calculations. A selection of results showing the effects of different approximations on ionization cross sections for K, L, and M shells is presented.

Compositional averaging of continuum intensities in multielement compounds.

We find no physical basis for traditional mass-fraction weighted averaging of X-ray continuum measured in pure elements to estimate continuum production from compounds. Measurements of continuum from pairs of stable isotopes demonstrate that mass alone (the presence of more or fewer neutrons) has no effect on continuum production in electron probe microanalysis. Electron-fraction weighted averaging, which is based on the relative contribution of each constituent element to the electron (or proton) composition of a compound, proved superior to mass-fraction weighted averaging, in predicting the continuum of a compound from the measured continuum of its elements.

Electron microscopy, micro-analysis, and X-ray diffraction characterization of the mineral-like tissue deposited by human cementum tumor-derived cells.

The nature and characteristics of the mineralized-like tissue deposited by cementoblasts are not well-known due to the difficulties in obtaining and culturing cells representing the cementum phenotype. We hypothesized that a putative cementoblastic cell line derived from a human cementoblastoma could serve as a suitable model to study the physical, chemical, and morphological features of the cementum-like tissue deposited in vitro. The cementoblastoma cell line was studied by transmission electron, high resolution, scanning, and atomic force microscopy and compared with human cellular cementum, human osteoblasts, and human alveolar bone. The analyses of the crystals and mineral-like tissue in the cell line were performed by x-ray diffraction microscopy and energy-dispersive x-ray micro-analysis. TEM examination of cementoblastoma cells revealed the presence of electron-dense intracellular vesicles surrounded by a membrane that contained filaments and needle-like structures. The diffraction patterns obtained from the intracellular material and human cellular cementum were similar, with D-spacings of 3.36 and 2.8, consistent with those of hydroxyapatite (3.440 and 2.814). The composition of the mineral-like tissue had a Ca/P ratio of 1.60 for cementoblastoma cells and 1.97 for human cellular cementum. Na (5.29%) and Cl (1.47%) were present in the composition of cementoblastoma cells. Human cellular cementum additionally contained Mg (4.95%). Osteoblastic cells showed a Ca/P ratio of 1.6280. Na represented 4.52% and Cl 1.22% of its composition. Human alveolar bone had a Ca/P ratio value of 2.01. Na (6.63%), Mg (2.10%), and Cl (0.84%) were also present. All samples examined represented biological-type hydroxyapatite. Based on the compositional and morphological features, these findings indicate that cementoblastoma-derived cells express the human cellular cementum phenotype.

Marginal seal composition in amalgam restored teeth of varying marginal leakage.

An in vitro study was performed to ascertain the marginal seal elemental composition of amalgam restored extracted teeth of known marginal leakage. Occlusal cavities were cut in 400 caries free extracted teeth and left unlined or lined with one of 5 bases. A varnish was applied to half the cavities followed by restoration with a low copper or high copper amalgam to produce 20 restoration combinations. The teeth were stored in 1 per cent NaCl and thymol for 3 and 12 months at 20 degrees C whereafter a standard fluorescent dye marginal leakage test was performed on 320 specimens (eight teeth per treatment). Restoration combinations were grouped into 4 seal classes depending on percentage marginal seal achieved for each combination: 0-25 per cent; 26-50 per cent; 51-75 per cent and 76-100 per cent. The 80 remaining teeth (2 teeth per treatment) were fractured to expose the restoration and cavity surface, covered with marginal seal material and this was analysed by energy dispersive X-ray analysis. Elemental seal composition was compared to percentage marginal seal achieved using ANOVA and Tukey's test with significance set at p < 0.05. Numbers of elemental analysis specimens falling into each marginal seal class was 0-25 per cent = 48; 26-50 per cent = 18; 51-75 per cent = 10; 76-100 per cent = 4. Of the 16 elements detected, nine were significantly linked to sealing/leakage: Ca, Cl, Cu, Mg, Hg, P, Ag, Sn and Zn. The findings have a bearing on the improved longevity of amalgam restorations.

The use of X-ray photoelectron spectroscopy for the study of oral streptococcal cell surfaces.

Physicochemical and structural properties of microbial cell surfaces play an important role in their adhesion to surfaces and are determined by the chemical composition of the outermost cell surface. Many traditional methods used to determine microbial cell wall composition require fractionation of the organisms and consequently do not yield information about the composition of the outermost cell surface. X-ray photoelectron spectroscopy (XPS) measures the elemental composition of the outermost cell surfaces of micro-organisms. The technique requires freeze-drying of the organisms, but, nevertheless, elemental surface concentration ratios of oral streptococcal cell surfaces with peritrichously arranged surface structures showed good relationships with physicochemical properties measured under physiological conditions, such as zeta potentials. Isoelectric points appeared to be governed by the relative abundance of oxygen- and nitrogen-containing groups on the cell surfaces. Also, the intrinsic microbial cell-surface hydrophobicity by water contact angles related to the cell-surface composition as by XPS and was highest for strains with an elevated isoelectric point. Inclusion of elemental surface compositions for tufted streptococcal strains caused deterioration of the relationships found. Interestingly, hierarchical cluster analysis on the basis of the elemental surface compositions revealed that, of 36 different streptococcal strains, only four S. rattus as well as nine S. mitis strains were located in distinct groups, well separated from the other streptococcal strains, which were all more or less mixed in one group.

X-ray-induced photoelectron spectroscopy of dentin as a function of duration of Ar(+)-ion etching.

XPS, or ESCA, measures the atomic concentration in the outermost layers of the sample. The surface is often etched with Ar(+)-ions before any measurement. We investigated the role thereof on XPS measurements of root dentin. Nine slices were cut from premolars. Slices were ground or broken. XPS was measured before etching. Six samples were then subjected to Ar(+)-ion etching (10 kV ions, 0.25 microA/mm2). A gold sample was also included. Relative concentrations of N and C decreased with etching time, while O, P, and Ca increased. N and C curves were analyzed assuming a sum of two exponential decays and a final level. On average, tau 1 = 20 sec for C and 17 sec for N. On average, tau 2 = 278 sec for C and 350 sec for N. No differences between differently prepared samples were apparent. The gold sample showed a single decay to noise for C and N, with tau 1 = 8 and 7 sec, respectively. We conclude that two decay processes are present, due to gas removal and to the removal of organic material from the dentin matrix, respectively. Thus, true values can be obtained by extrapolation to t = 0 of only the data obtained by summing the slow decay and the final level.

Electron probe microanalysis and transverse microradiography studies of artificial lesions in enamel and dentin: a comparative study.

In cardiology and research involving the interactions between restorative materials and dental hard tissues, it is important for small changes in tooth mineral content to be measurable. Currently, transverse microradiography (TMR) is the most accepted tool for the above purpose. Electron Probe Microanalysis (EPMA) can yield both qualitative identification of elements and quantitative compositional information. The purpose of this study was to compare the mineral distribution in well-defined artificial lesions, in dentin and enamel, by the use of both TMR and EPMA on the same sample. The good correlation between the two sets of data validates EPMA as a technique and helps in the interpretation of its results. The data from TMR analysis are expressed as vol% of mineral, while EPMA gives the levels of Ca and phosphate in wt%. The conversion between the two sets of data is complicated by the fact that local density is, as yet, unknown.

[The concentration levels of airborne quartz at an urban site]. / Livelli di concentrazione del quarzo aerodisperso in un sito urbano.

The IARC has recently included crystalline silica among substances considered carcinogenic for man. This new evaluation immediately posed the need to measure the exposure levels of the general population. The paper reports the results of measurements of the concentrations of quartz (i.e., the most common form of crystalline silica) in a location in the urban area of Rome. First we studied the respirable fractions of the airborne particles (PM10) sampled in the Spring of 1996 with a cascade impactor, which were characterized using a scanning electron microscope equipped with an X-ray microprobe. Ten components were identified including total silica (crystalline and amorphous), which was present in a percentage of 3.7% on average. On the basis of these data a methodological study was undertaken of the concentration of quartz in the historic series of PM10 sampled daily at the same site by means of an AMP instrument (Airborne Particles Monitor). The filters of mixed cellulose esters on which the PM10 was collected were incinerated at low temperature in oxygen plasma to eliminate the organic component. The residue was deposited on silver filters which were read with a conventional X-ray diffractometer in order to determine the quantity of quartz. We analyzed 28 filters from four representative weeks of the four seasons of 1994, the year in which systematic sampling was initiated. The results showed a mean weekly concentration of airborne quartz of between 0.6 and 1.5 micrograms/Nmc, which gives a percentage over PM10 of 1.7 and 3.4 respectively. These data substantially agree with previous results obtained with electron microscopy and show that the levels of quartz in the urban atmosphere under study were about one hundred times lower than the TLV currently recommended by the ACGIH for working environments (100 micrograms/Nmc) and which are also in force in Italy.

Scanning and electron microprobe analysis of metal-porcelain interface.

The purpose of this study was to analyze the interfacial region between porcelain and base metal alloy using scanning electron microscope with electron microprobe analyzer. Results gave evidence of formation of Nio and Cr2O3 with evidence of more migration of NiO towards the porcelain. Sandblasting of oxidized and fired metal samples (simulating firing of porcelain without its application) showed appearance of crystalline structure of Ni and Cragain, indicating delamination of oxide layer by sandblasting. At porcelain side analysis showed NiO and Cr2O3 and iron oxide plus Si, K, CI, Sn and Cu.

Embedding resin space, water contents and chromatin compaction in rabbit sperm nuclei: electron microscopic X-ray spectrophotometry of a brominated probe.

EPON labelled with bromide was used to embed ejaculated rabbit spermatozoa, with the hypothesis that it replaces cell water. X-Ray spectrophotometric microanalysis of sperm nuclei, of egg yolk (an internal standard containing roughly 50% water) and of surrounding embedding resin, revealed that a part of the bromide was bound to the biological components. These latter were saturated when bromide was added in higher concentrations, and the increase in measured bromide could be used to calculate absolute resin contents in sperm nuclei which gives a mean value of 22.62%. Most nuclei (60.80%) were well condensed and displayed a mean resin space close to 17% of the total nuclear volume. The less condensed nuclei had a mean resin space close to 28%. The use of an internal standard revealed that calculated values were underestimated by 4%.

Energy-dispersive X-ray analysis and scanning electron microscopy of pleura. Study of reference, exposed non-pneumoconiotic, and silicotic populations.

Inorganic element content in pleura and lung was studied by energy-dispersive X-ray analysis (EDXA) and scanning electron microscopy (SEM) in reference, exposed non-pneumoconiotic, and silicotic populations. Samples of parietal pleura, visceral pleura, and lung in 11 subjects with no measurable exposure to inorganic dust and of visceral pleura and lung samples of 10 exposed non-pneumoconiotic individuals and eight silicotic patients were examined. Constant depositions of silicon and calcium were detected in visceral pleura, parietal pleura, and lung of the reference group and in visceral pleura and lung of the exposed non-pneumoconiotic and silicotic groups. Other elements, such as aluminum and iron, were also detected in the exposed non-pneumoconiotic and silicotic patients and, less frequently, in the reference group. There was no difference in silicon content between parietal and visceral pleura in the reference group. Silicon content in silicotic patients was higher and more irregularly distributed in the pleura (p = 0.005 and p < 0.01, respectively) and in the lung (p = 0.005 and p < 0.01, respectively) than in the reference group. Comparison of the silicon content in pleura between silicotic and exposed non-pneumoconiotic subjects showed a nonsignificant probability of difference (p = 0.052), whereas there were no differences with respect to the silicon content in lung. There were no differences in the pleural and lung silicon content between the exposed non-pneumoconiotic and reference groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Fluoride profiles of enamel following topical application of neutral and acidulated NaF solution using x-ray photoelectron spectroscopy (ESCA)--an in vitro study.

An in vitro analysis of fluoride in the surface enamel using x-ray photo-electron spectroscopy carried out on sound untreated teeth, sound teeth treated with neutral NaF and acidulated NaF and teeth with artificial caries treated with NaF and acidulated NaF revealed Ca/F ratio at surface and 360 degrees A as 0.140:1 and 0.140:1; 0.636:1 and 0.192:1; 1.112:1 and 0.908:1. 1.2:1 and 1.289:1; 2.11:1 and 1.87:1 respectively.