Carlos A. Pérez

Synchrotron radiation X-Ray fluorescence at the LNLS: beamline instrumentation and experiments

The x-ray fluorescence heamline of the Laboratorio Nacional de Luz Sincrotron (LNLS) is described. The main optical component of the beamline is a silicon (111) channel-cut monochromator, which can tune energies between 3 and 14 keV. A general description of two experimental stations is given. Beam characterization was done by measuring experimental parameters such as vertical profile and monochromatic flux. These results show that the photon flux at 8 keV in an area of 20 mm 2 is 4.2 × 10 9 photons s -1 . The possibility of achieving fine tuning of energies (high resolution) was confirmed. This paper presents some original results derived from the commissioning of the beamline, such as a comparison of detection limits in different experimental conditions, and a novel mechanical system to align capillaries together with a semi-automatic adjustment procedure. So far, there have been several proposals to perform a variety of experiments at this beamline, covering different fields, such as physics, chemistry, geology and biology.

Analytical approach to the metallomic of Nile tilapia (Oreochromis niloticus) liver tissue by SRXRF and FAAS after 2D-PAGE separation: Preliminary results

An investigation was made into calcium, iron and zinc in protein spots in samples of Nile tilapia (Oreochromis niloticus) liver tissue obtained after protein separation by two-dimensional polyacrylamide gel electrophoresis (2D-PAGE) and subsequent qualitative and quantitative evaluation by synchrotron radiation X-ray fluorescence (SRXRF) and Flame Atomic Absorption Spectrometry (FAAS). An analysis of the fluorescence spectra indicated the presence of calcium, iron and zinc in 12, 6 and 8 liver protein spots, respectively. The metal ions found were distributed mainly in proteins with a molar mass of less than 40.00 kDa and more than 12.00 kDa, with pI in the range of 4.70-9.40. The only exception was a spot presenting protein with a molar mass of 10.10 kDa. In addition to calcium, iron and zinc, sulfur and phosphorus - which are non-metals that may be part of the protein structure, were also detected. After microwave-assisted acid mineralization of the proteins spots, a FAAS estimation of the concentration of calcium, iron and zinc ions bound to these proteins indicated a range of 1.08-5.80 mg g(-1), 2.02-8.03 mg g(-1) and 1.60-8.55 mg g(-1), respectively.

Association between As and Cu renal cortex accumulation and physiological and histological alterations after chronic arsenic intake.

Arsenic (As) is one of the most abundant hazards in the environment and it is a human carcinogen. Related to excretory functions, the kidneys in humans, animal models or naturally exposed fauna, are target organs for As accumulation and deleterious effects. Previous studies carried out using X-ray fluorescence spectrometry by synchrotron radiation (SR-microXRF) showed a high concentration of As in the renal cortex of chronically exposed rats, suggesting that this is a suitable model for studies on renal As accumulation. This accumulation was accompanied by a significant increase in copper (Cu) concentration. The present study focused on the localization of these elements in the renal cortex and their correlation with physiological and histological As-related renal effects. Experiments were performed on nine male Wistar rats, divided into three experimental groups. Two groups received 100 microg/ml sodium arsenite in drinking water for 60 and 120 consecutive days, respectively. The control group received water without sodium arsenite (< 50 ppb As). For histological analysis, 5-mum-thick sections of kidneys were stained with hematoxylin and eosin. Biochemical analyses were used to determine concentrations of plasma urea and creatinine. The As and Cu mapping were carried out by SR-microXRF using a collimated white synchrotron spectrum (300 microm x 300 microm) on kidney slices (2 mm thick) showing As and Cu co-distribution in the renal cortex. Then, renal cortical slices (100 microm thick) were scanned with a focused white synchrotron spectrum (30 microm x 30 microm). Peri-glomerular accumulation of As and Cu at 60 and 120 days was found. The effects of 60 days of arsenic consumption were seen in a decreased Bowmans space as well as a decreased plasma blood urea nitrogen (BUN)/creatinine ratio. Major deleterious effects; however, were seen on tubules at 120 days of exposition. This study supports the hypothesis that tubular accumulation of As-Cu may have some bearing on the arsenic-associated nephrotoxicological process.

X-ray resonant Raman scattering cross sections of Mn, Fe, Cu and Zn

X-ray fluorescence spectra present singular characteristics produced by the different scattering processes. When atoms are irradiated with incident energy lower and close to an absorption edge, scattering peaks appear due to an inelastic process known as resonant Raman scattering. It constitutes an important contribution to the background of the fluorescent line. The resonant Raman scattering must be taken into account in the determination of low concentration contaminants, especially when the elements have proximate atomic numbers. The values of the mass attenuation coefficients experimentally obtained when materials are analysed with monochromatic x-ray beams under resonant conditions differ from the theoretical values (between 5% and 10%). This difference is due, in part, to the resonant Raman scattering. Monochromatic synchrotron radiation was used to study the Raman effect on pure samples of Mn, Fe, Cu and Zn. Energy scans were carried out in different ranges of energy near the absorption edge of the target element. As the Raman peak has a non-symmetric shape, theoretical models for the differential cross section, convoluted with the instrument function, were used to determine the RRS cross section as a function of the incident energy.

Elemental mapping of teeth using μSRXRF

Human teeth were analysed by X-ray microfluorescence analysis using synchrotron radiation (μSRXRF). The aim of this work was to study the elemental distribution for Ca, Zn and Sr along the dental regions, enamel, dentine and pulp from patterns of relative fluorescence intensities. The measurements were performed in standard geometry of 45° incidence, exciting with a white beam and using a conventional system collimation (orthogonal slits) in the XRF beamline at the Synchrotron Light National Laboratory (Campinas, Brazil). The results show that Ca distribution is quite constant and it is independent of the tooth type and individuals characteristics. An increase of the Zn concentration was found for the pulp region and for untreated carious areas. Ca and Sr distributions show a similar behavior.

Microscopic X-ray fluorescence analysis of human dental calculus using synchrotron radiation

In this work, new results of one- and two-dimensional spatial distributions of major, minor and trace elements of human dental calculus are presented. X-ray fluorescence induced by a synchrotron radiation source was used. The measurements were carried out in the X-ray microprobe station mounted at the X-ray fluorescence beamline of the Brazilian National Synchrotron Light Laboratory (LNLS). Two-dimensional distributions show that calcium, the major element in this type of sample, has a uniform pattern over the mapped area, while trace elements are non-homogeneously distributed. By means of different linear scans along the growing axis of the dental calculus, a markedly spatial correlation between Cu and Zn was found. A semi-quantitative analysis for Cu and Zn was performed by means of calibration curves using appropriate fabricated standards. The concentration values found for these metals were higher than those obtained in conventional bulk analysis. It was observed that these metals accumulated preferentially in the subgingival part of the calculus, near the tooth surface. These results indicate that the mineralization processes, which take place for both type of calculus, are essentially different.

Zinc incorporation in human dental calculus.

We present here the first study of the local environment of zinc ions in biological calcium phosphates. It was suggested from in vitro studies that zinc inhibits the formation of hydroxyapatite and promotes the formation of more soluble phases, like tricalcium phosphate. Several mechanisms of zinc - calcium phosphate interaction were proposed, yielding either to the adsorption or to the incorporation of zinc ions into the phosphate structure. The results obtained here show that, under in vivo conditions, the zinc atoms are fully incorporated into the crystalline structure of the calcium phosphates.

Anisotropic angular distribution of Er L x-rays following photoionization by linearly polarized radiation

The angular distribution of the Er L emission after photoionization by linearly polarized monochromatic synchrotron radiation has been measured. A dedicated instrumentation, designed for this kind of experiment, allowed observation of even the smallest anisotropy of the line. The experimental anisotropy parameter and degree of alignment parameter show very good agreement with the predicted theoretical values. It has been found that the ion alignment with the incident beam direction is a function of the polarization of the incident beam. Evidence of non-dipole contributions was observed.

SRXRF analysis with spatial resolution of dental calculus

This work presents elemental-composition studies of dental calculus by X-ray fluorescence analysis using synchrotron radiation. The intrinsic characteristics of synchrotron light allow for a semi-quantitative analysis with spatial resolution. The experiments were carried out in the high-vacuum station of the XRF beamline at the Synchrotron Light National Laboratory (Campinas, Brazil). All the measurements were performed in conventional geometryO45∞a 45∞U and the micro-collimation was attained via a pair of orthogonal slits mounted in the beamline. In this way, pixels of 50 lm 50 lm were obtained keeping a high flux of photons on the sample. Samples of human dental calculus were measured in diAerent positions along their growing axis, in order to determine variations of the compositions in the pattern of deposit. Intensity ratios of minor elements and traces were obtained, and linear profiles and surface distributions were determined. As a general summary, we can conclude that lXRF experiments with spatial resolution on dental calculus are feasible with simple collimation and adequate positioning systems, keeping a high flux of photon. These results open interesting perspectives for the future station of the line, devoted to lXRF, which will reach resolutions of the order of 10 lm. ” 2000 Elsevier Science B.V. All rights reserved.

Heart fossilization is possible and informs the evolution of cardiac outflow tract in vertebrates

Elucidating cardiac evolution has been frustrated by lack of fossils. One celebrated enigma in cardiac evolution involves the transition from a cardiac outflow tract dominated by a multi-valved conus arteriosus in basal actinopterygians, to an outflow tract commanded by the non-valved, elastic, bulbus arteriosus in higher actinopterygians. We demonstrate that cardiac preservation is possible in the extinct fish Rhacolepis buccalis from the Brazilian Cretaceous. Using X-ray synchrotron microtomography, we show that Rhacolepis fossils display hearts with a conus arteriosus containing at least five valve rows. This represents a transitional morphology between the primitive, multivalvar, conal condition and the derived, monovalvar, bulbar state of the outflow tract in modern actinopterygians. Our data rescue a long-lost cardiac phenotype (119-113 Ma) and suggest that outflow tract simplification in actinopterygians is compatible with a gradual, rather than a drastic saltation event. Overall, our results demonstrate the feasibility of studying cardiac evolution in fossils. DOI: http://dx.doi.org/10.7554/eLife.14698.001