Biomedical subjects

Gerald Falkenberg

Publications and source records attributed to Gerald Falkenberg.

6 recordsLinked to original sources

PubMed2006

Investigations of differences in iron oxidation state inside single neurons from substantia nigra of Parkinson's disease and control patients using the micro-XANES technique.

X-ray absorption near edge structure spectroscopy was applied in order to investigate differences in iron chemical state between the nerve cells of substantia nigra (SN) representing Parkinson's disease (PD) and those of control cases. Autopsy samples were cut using a cryotome, and were not fixed and not embedded in paraffin. The comparison of the absorption spectra near the iron K-edge measured in melanized neurons from SN of PD and control samples did not show significant differences in iron oxidation state. Measurements of inorganic reference materials containing iron in the second and third oxidation states indicate that most of the iron in all the nerve cell bodies examined was oxidized and occurred as trivalent ferric iron (Fe(3+)).

Humans↗

PubMed2006

In vivo investigation of the distribution and the local speciation of selenium in Allium cepa L. by means of microscopic X-ray absorption near-edge structure spectroscopy and confocal microscopic X-ray fluorescence analysis.

In this work, microscopic X-ray absorption near-edge structure spectroscopy (mu-XANES) and confocal microscopic X-ray fluorescence analysis (mu-XRF) were used for the in vivo determination of the distribution of total selenium and for the local speciation of selenium in roots and leaves of onion. Selected Allium cepa L. plants were grown hydroponically in a standard medium containing inorganic selenium compounds (selenite or selenate). The measurements were performed in vivo, that is, on living plants without the need for any form of sampling or sample pretreatment and without the necessity for cutting plant tissues into pieces. Distinct energy differences of the XANES spectra of various selenium reference compounds having different oxidation states allow adjusting the excitation energies used for mu-XRF mapping in such a manner that the distribution of selenium in various oxidation states is obtained with a spatial resolution of a few tens of micrometers within the virtual cross section of the onion tissues. We find that the ratio of inorganic to amino acid selenium compounds differs in various subparts of the plant. Detailed in vivo investigation of the distribution of various selenium species in virtual cross sections of root tips and green leaf shows that the selenium transport takes place via different mechanisms, depending on the nature of the selenium compounds originally taken up.

Amino Acids↗

PubMed2006

Microprobe techniques for speciation analysis and geochemical characterization of mine environments: the mercury district of Almadén in Spain.

Metallurgic calcines with very high mercury and methylmercury content from the Almadén mining district were analyzed by synchrotron-based microprobe techniques. Information about mercury speciation was obtained by micro-EXAFS (microscopic extended X-ray absorption fine structure) spectroscopy, whereas elemental associations were evaluated by micro-XRF (microscopic X-ray fluorescence analysis) mapping. Complementary characterization methodologies, including X-ray diffraction (XRD), inductively coupled plasma-optical spectroscopy (ICP-OES), as well as a sequential extraction scheme (SES), were used to predict the potential availability of mercury. Analysis of total metal content revealed extremely high concentrations of mercury and iron (between 7 and 35 and 65-70 g kg(-1), respectively) and high zinc concentrations (2.2-2.5 g kg(-1)), whereas other metals such as copper, nickel, and lead were found at low concentration levels (30-300 mg kg(-1)). Micro-EXAFS results indicate that cinnabar (HgS(red)) is one of the main species within the studied mercury-rich particles (5-89% of total mercury content), together with more soluble mercury compounds such as Hg3(SO4)02 (schuetteite) and HgO (5-55% of total mercury content). Additionally, element-specific micro-XRF maps of selected mercury-rich particles in the studied samples revealed an evident correlation among Hg-Pb-Ni (and S), indicating a possible geochemical linkage of these elements. Correlations were also found among Fe-Mn and Hg, which have been attributed to sorption of mercury onto oxyhydroxides of Fe and Mn. This finding was supported by results from a sequential extraction scheme, where a significant

Environmental Monitoring↗

PubMed2005

Trace metals in ambient air: Hourly size-segregated mass concentrations determined by synchrotron-XRF.

Trace metals are ubiquitous in urban ambient air, with mass concentrations in the range of a few microg/m3 down to less than 100 pg/m3. To measure such low concentrations represents a challenge for chemical and physical analysis. In this study, ambient aerosol was collected in Zürich (Switzerland) in 1-h intervals and three size fractions (aerodynamic diameters 0.1-1 microm, 1-2.5 microm, and 2.5-10 microm), using a three-stage rotating drum impactor (RDI). The samples were analyzed by energy-dispersive Synchrotron radiation X-ray fluorescence spectrometry (SR-XRF) to obtain size-segregated hourly elemental aerosol mass concentrations for Cr, Mn, Fe, Cu, Zn, Br, and Pb, along with S, Cl, and Ca under the selected experimental conditions. The high sensitivity of SR-XRF allowed for detection limits of <50 pg/m3 for most of the above elements, with a net analysis time of only 15 s per sample. The data obtained with this technique illustrate that there is a considerable gain of relevant information when time resolution for measurements is increased from 1 day to 1 h. The individual size fractions of a specific element may show significantly different short-term patterns.

Aerosols↗

PubMed2005

Direct analysis of Al2O3 powders by total reflection X-ray fluorescence spectrometry.

A direct analysis procedure for the determination of trace impurities of Ca, V, Cr, Mn, Fe, Ni, Cu, Zn and Ga in Al2O3 ceramic powders by total reflection X-ray fluorescence spectrometry (TXRF) is described. The powders were analysed in the form of slurries containing 1-10 mg mL(-1) of powder. The use of the procedure in the case of powders with differing grain size and for different slurry concentrations was investigated. Three different quantification possibilities were compared, namely the use of Al as a matrix component, the use of Fe as a trace element contained in the sample or of Co added in concentrations of 200 microg g(-1) as internal standard. The homogeneity of elemental distributions in sample layers deposited on the TXRF quartz carriers by evaporating 5 microL of the 10 mg mL(-1) slurries was studied by scanning the 4- to 5-mm-diameter spots of two samples by synchrotron radiation TXRF at Hasylab. For powders with differing graininess but mainly finer than about a few 10 microm, no systematic influence of the grain size on the accuracy of the determinations of Ca, V, Fe, Ni, Cu and Zn could be observed. The measurement precision, however, seemed to be limited by inhomogeneous distributions of the trace elements in the samples as testified by the synchrotron radiation TXRF scans. Detection limits of the developed TXRF procedure for Ca, V, Cr, Mn, Fe, Ni, Cu, Zn and Ga were found to be in the 0.3-7 microg g(-1) range and were shown to increase slightly with the grain size of the samples. Quantification using Al (matrix) as internal standard led to systematically higher values out of the accuracy required, whereas the other two approaches in all cases led to reliable results.

Aluminum Oxide↗

PubMed2004

Three-dimensional trace element analysis by confocal X-ray microfluorescence imaging.

A three-dimensional (3D) variant of scanning micro X-ray fluorescence (XRF) is described and evaluated at the ID18F instrument of the European Synchrotron Radiation Facility (ESRF). The method is based on confocal excitation/detection using a polycapillary half-lens in front of the energy-dispersive detector. The experimental arrangement represents a significant generalization of regular two-dimensional (2D) scanning micro-XRF and employs a detector half-lens whose focus coincides with that of the focused incoming beam. The detection volume defined by the intersection of the exciting beam and the energy-dependent acceptance of the polycapillary optics is 100-350 mum(3). Minimum detection limits are sub-ppm, and sensitivities are comparable with regular scanning XRF. Next to the reduction of in-sample single/multiple scattering, the setup provides the possibility of sample depth scans with an energy-dependent resolution of 10-35 mum in the energy range of 3-23 keV and the possibility of performing 3D-XRF analysis by simple XYZ linear scanning. This provides a suitable alternative to X-ray fluorescence tomography. The method is illustrated with results of the analysis of solid inclusions in diamond and fluid inclusions in quartz.

Journal Article↗