Optimization of L‐shell X‐ray fluorescence detection of lead in bone phantoms using synchrotron radiation

Closely related toxicity and retention mechanisms of lead (Pb) in the human body involve the bone tissues where Pb can accumulate and reside on a time scale ranging from years to tens of years. In vivo measurements of bone Pb can, therefore, play an important role in a comprehensive health risk assessment of Pb exposure. In vivo L‐shell X‐ray fluorescence (LXRF) measurement of bone Pb was first demonstrated over 4 decades ago. Implementation of the method, however, encountered challenges associated with low sensitivity and calibration procedure. In this study, the LXRF measurement was optimized by varying the incident photon energy and the excitation‐detection geometry. The Canadian Light Source synchrotron radiation was used to compare 2 different excitation‐detection geometries of 90^° and 135^° using 3 different X‐ray photon energies: 15.8, 16.6, and 17.5 keV. These energies optimized excitation of the L₃ subshell of Pb and simulated the most intense K‐shell emissions of zirconium, niobium, and molybdenum, respectively. Five rectangular plaster‐of‐Paris bone phantoms with Pb concentrations of 0, 7, 17, 26, and 34 μg/g, and one rectangular 3.1‐mm‐thick resin phantom mimicked the X‐ray attenuation properties of human bone and soft tissue, respectively. Optimal LXRF detection was obtained by the 15.8‐keV energy and the 90^° and 135^° geometries for the bare bone and the bone and soft tissue phantoms, respectively.     

Lead concentration in feces and urine of exposed rats by x‐ray fluorescence and electrothermal atomic absorption spectrometry

Measurements made in feces and urine of Wistar rats exposed to lead acetate (n = 20) in drinking water since the fetal period were compared with those obtained from a control group (n = 20) in order to assess the age influence on Pb excretion. The measurements were made in different collections of rats aging between 1 and 11 months. To determine the Pb content of the samples, total reflection X‐ray fluorescence (TXRF) and electrothermal atomic absorption spectrometry (ETAAS) were used for the urine samples and energy dispersive X‐ray fluorescence (EDXRF) was used for the feces. The results show high concentrations of Pb being eliminated from the organism by urine and feces in contaminated rats. Values vary from (600 ± 140) µg l^?1 to (5 460 ± 115) µg l^?1 in urine and from (4 500 ± 300) µg g^?1 to (11 400 ± 3 300) µg g^?1 in dry feces. The control rats show, in general, low lead concentrations or below detection limits. The fecal/urinary ratio was studied. It was shown to be about three to four orders of magnitude and positively correlated with time. It was verified in feces and urine that excretion decreases with the animal age and that this decrease is made by different levels of excretion. The excretions of Pb in urine and in feces are positively correlated. A good agreement was found between the results obtained with TXRF and ETAAS for urine samples. This work also stresses the suitability of these techniques in the study of Pb intoxication. Copyright © 2011 John Wiley & Sons, Ltd.     

Development of a K‐shell x‐ray fluorescence measurement of cadmium in bone

Cadmium is known to accumulate in the human body and chronic exposures have been clearly linked to adverse health effects, showing the kidney as the critical target organ. However, there is evidence of an association between extensive environmental exposure to cadmium and alterations in bone/calcium metabolism. Therefore, it is desirable to be able to measure bone cadmium non‐invasively in humans. Tibia was selected as a measurement site and source‐excited K‐shell x‐ray fluorescence was investigated both experimentally and computationally. Initially the 88 keV γ‐rays from ¹⁰⁹Cd were used to assess minimum detectable level (MDL) of cadmium in phantoms comprising plaster of Paris (bone) and wax (soft tissue). An MDL of 3–4µg g^?1 was achieved for overlying tissue thicknesses of up to 5 mm. Alternative sources were ¹²⁵I and ²⁴¹Am. Monte Carlo simulation showed that the spectral contrast for ¹²⁵I would be poor. The 60 keV γ‐rays from ²⁴¹Am were more promising, provided that the 26 keV γ‐rays were filtered out. Experiments with ²⁴¹Am confirmed that a lower MDL could be achieved. However, the product of MDL and square root of dose (a figure of merit) was not improved. Since effective doses for these source‐excited x‐ray fluorescence procedures are low (typically of the order of 0.1 µSv or less), it may be that lower MDL would be preferred over lower dose. Nevertheless, development continues as a further reduction in MDL is highly desirable. Copyright © 2005 John Wiley & Sons, Ltd.     

Determination of Cr(III) and Cr(VI) in water by wavelength‐dispersive X‐ray fluorescence spectrometry after preconcentration with an ion‐exchange resin disk

A rapid and simple method using an ion‐exchange resin disk combined with wavelength‐dispersive X‐ray fluorescence (WDXRF) spectrometry was developed for the determination of Cr(III) and Cr(VI) in water. A 100‐ml water sample was first adjusted to pH 3 with nitric acid and then passed through an anion‐exchange resin disk placed on top of a cation‐exchange resin disk at a flow rate of 1 ml min^?1 to separate Cr(III) and Cr(VI). Anionic Cr(VI) was preconcentrated on the upper anion‐exchange resin disk, whereas cationic Cr(III) was preconcentrated on the lower cation‐exchange resin disk. Each ion‐exchange resin disk was dried at 100 °C for 30 min in an electric oven and coated with a commercially available laminate film. The specimens were measured using a WDXRF spectrometer. The calibration curves of Cr(III) and Cr(VI) showed good linearity in the range 1–10 µg. The detection limits corresponding to three times the standard deviation (n = 5) of blank values were 0.17 µg for Cr(III) and 0.16 µg for Cr(VI). If a 1‐l water sample is used, these limits would be 0.17 and 0.16 µg l^?1, respectively. A spike test for 50 µg l^?1 Cr(III) and Cr(VI) in tap water and river water showed quantitative recoveries (94–114%), although this was not observed for mineral drinking water owing to the overlap of V Kβ with Cr Kα. The recovery after overlap correction was satisfactory (115%). Copyright © 2011 John Wiley & Sons, Ltd.     

High‐flux hard X‐ray microbeam using a single‐bounce capillary with doubly focused undulator beam

A pre‐focused X‐ray beam at 12 keV and 9 keV has been used to illuminate a single‐bounce capillary in order to generate a high‐flux X‐ray microbeam. The BioCAT undulator X‐ray beamline 18ID at the Advanced Photon Source was used to generate the pre‐focused beam containing 1.2 × 10¹³ photons s^?1 using a sagittal‐focusing double‐crystal monochromator and a bimorph mirror. The capillary entrance was aligned with the focal point of the pre‐focused beam in order to accept the full flux of the undulator beam. Two alignment configurations were tested: (i) where the center of the capillary was aligned with the pre‐focused beam (`in‐line') and (ii) where one side of the capillary was aligned with the beam (`off‐line'). The latter arrangement delivered more flux (3.3 × 10¹² photons s^?1) and smaller spot sizes (≤10 µm FWHM in both directions) for a photon flux density of 4.2 × 10¹⁰ photons s^?1µm^?2. The combination of the beamline main optics with a large‐working‐distance (approximately 24 mm) capillary used in this experiment makes it suitable for many microprobe fluorescence applications that require a micrometer‐size X‐ray beam and high flux density. These features are advantageous for biological samples, where typical metal concentrations are in the range of a few ng cm^?2. Micro‐XANES experiments are also feasible using this combined optical arrangement.     

Transportable EDXRF analysis of environmental water samples using Amberlite IRC748 ion‐exchange preconcentration

Transportable energy‐dispersive X‐ray fluorescence spectrometers allow on‐site assessment of metal‐contaminated soils, sediments and other solids. Multi‐element analysis of liquid samples, such as surface water, groundwater, acid leach and aqueous soil extracts, would enhance on‐site environmental assessments. However, transportable spectrometers typically have detection limits for metals in waters of approximately 1–10 mg l^?1, whereas many toxic elements are regulated at concentrations of 1–100 µg l^?1. If detection limits for this technique can be lowered, then only one analytical tool, a transportable XRF spectrometer, may be sufficient for remote areas, increasing program flexibility and reducing the amount of equipment that needs to be purchased, transported and operated. This research develops an in‐field preconcentration technique using Amberlite IRC748 cation‐exchange resin, followed by XRF analysis of Fe, Ni, Cu, Zn and Pb at µg l^?1 concentrations in aqueous samples. The operational parameters tested to maximise analyte recovery included flow rate, and the mass and chemical form of the resin. The method was tested with extracts from landfill soils and surface waters from a derelict base metal mine. The method recovered Cu, Zn and Pb accurately, and Ni and Fe at concentrations satisfactory for screening purposes. Copyright © 2010 John Wiley & Sons, Ltd.     

XRF analysis of arsenic‐doped skin phantoms

Chronic arsenic poisoning can lead to serious health problems including vascular disorders and cancer. Therefore, the development of a system to measure arsenic in vivo would be useful in monitoring exposure. In particular, as skin is one of the tissues in which arsenic has health consequences and is stored for a prolonged period of time, an in vivo measure of skin arsenic content would be a clinically useful measure of chronic exposure. The preliminary development of an x‐ray fluorescence system to measure arsenic in vivo is reported. Standard addition arsenic‐ doped polyester resin phantoms were prepared, and the fluorescence induced by silver K x‐rays from a ¹⁰⁹Cd source was measured. Preliminary estimates of detection limits for an 8 mm thick phantom and an effective dose of ～0.3 µSv are 3.5 ± 0.2 and 10.3 ± 0.5 ppm in 90 and 180° measurement geometries, respectively, for a measurement time of 30 min. Copyright © 2004 John Wiley & Sons, Ltd.     

Design of an ultrahigh‐energy‐resolution and wide‐energy‐range soft X‐ray beamline

A new ultrahigh‐energy‐resolution and wide‐energy‐range soft X‐ray beamline has been designed and is under construction at the Shanghai Synchrotron Radiation Facility. The beamline has two branches: one dedicated to angle‐resolved photoemission spectroscopy (ARPES) and the other to photoelectron emission microscopy (PEEM). The two branches share the same plane‐grating monochromator, which is equipped with four variable‐line‐spacing gratings and covers the 20–2000 eV energy range. Two elliptically polarized undulators are employed to provide photons with variable polarization, linear in every inclination and circular. The expected energy resolution is approximately 10 meV at 1000 eV with a flux of more than 3 × 10¹⁰ photons s^?1 at the ARPES sample positions. The refocusing of both branches is based on Kirkpatrick–Baez pairs. The expected spot sizes when using a 10 µm exit slit are 15 µm × 5 µm (horizontal × vertical FWHM) at the ARPES station and 10 µm × 5 µm (horizontal × vertical FWHM) at the PEEM station. The use of plane optical elements upstream of the exit slit, a variable‐line‐spacing grating and a pre‐mirror in the monochromator that allows the influence of the thermal deformation to be eliminated are essential for achieving the ultrahigh‐energy resolution.     

Ultra‐thin optical grade scCVD diamond as X‐ray beam position monitor

Results of measurements made at the SIRIUS beamline of the SOLEIL synchrotron for a new X‐ray beam position monitor based on a super‐thin single crystal of diamond grown by chemical vapor deposition (CVD) are presented. This detector is a quadrant electrode design processed on a 3 µm‐thick membrane obtained by argon–oxygen plasma etching the central area of a CVD‐grown diamond plate of 60 µm thickness. The membrane transmits more than 50% of the incident 1.3 keV energy X‐ray beam. The diamond plate was of moderate purity (～1 p.p.m. nitrogen), but the X‐ray beam induced current (XBIC) measurements nevertheless showed a photo‐charge collection efficiency approaching 100% for an electric field of 2 V µm^?1, corresponding to an applied bias voltage of only 6 V. XBIC mapping of the membrane showed an inhomogeneity of more than 10% across the membrane, corresponding to the measured variation in the thickness of the diamond plate before the plasma etching process. The measured XBIC signal‐to‐dark‐current ratio of the device was greater than 10⁵, and the X‐ray beam position resolution of the device was better than a micrometer for a 1 kHz sampling rate.     

Automated Online Preconcentration System for the Determination of Trace Amounts of Lead Using Pb‐Selective Resin and Inductively Coupled Plasma–Atomic Emission Spectrometry

Abstract

An automated sequential‐injection online preconcentration system was developed for the determination of lead by inductively coupled plasma–atomic emission spectrometry (ICP‐AES). The preconcentration of lead was performed with a minicolumn containing a lead‐selective resin, Analig Pb‐01, which was installed between a selection and a switching valve. In an acidic condition (pH 1), lead could be adsorbed on the resin. The concentrated lead was afterward eluted with 25 µL of 0.06 M nitrilotriacetic acid (NTA) solution (pH 9) and was subsequently transported into the nebulizer of ICP‐AES for quantification. The selectivity of the resin toward lead was examined using a solution containing a mixture of 61 elements. When a sample volume of 5 mL was used, the quantitative collection of lead (≥97%) was achieved, along with an enrichment factor of 19, a sampling frequency of 12 samples hr^?1, a detection limit of 70 pg mL^?1, and a lowest quantification limit of 100 pg mL^?1. The linear dynamic range was 0.1 to 5 ng mL^?1, and the relative standard deviation (n=9) was 0.5% at a 5 ng mL^?1 Pb level. The detection limit of 30 pg mL^?1 and lowest quantification limit of 50 pg mL^?1 could be achieved when 10 mL of sample volume was used. The accuracy of the proposed method was validated by determining lead in the standard reference material of river water (SLRS‐4), and its applicability to the determination of lead in environmental river water samples was demonstrated.     

Proton µ‐PIXE mapping,AFM imaging and size statistics of mineral granules in a dental composite

We applied proton microbeam particle‐induced X‐ray emission (µ‐PIXE) for mapping Ca, Zr, Ba and Yb, and atomic force microscopy (AFM) for imaging the surface landscape of a dental composite which releases Ca²⁺ and F^? for the protection of hard dental tissues. Three areas ～250 × 250 µm² located ～0.5–2 mm apart on a smooth surface specimen were mapped with 3.1 MeV protons focused to a ～3.0 µm spot and at ～3.9 µm pixel size sampling. The maps evidenced particles with diameters of 3.2–32 µm (Ca), 20–60 µm (Zr), ≤ 4 µm (Ba) and 10–50 µm (Yb). Cross‐section area histograms of Ca‐rich particles fitted with 2–6 Poisson functions revealed a polydisperse size distribution and substantial differences from an area to another, possibly implying large local variations of Ca²⁺ released in the hard tissue near a dental filling of a few millimeters in diameter. Such imbalances may lead to low local Ca²⁺ protection of the dental tissue, favoring the onset of secondary caries. Similarly, AFM images showed high zone‐dependent differences in the distributions of grains with apparent diameters of 1–4 µm, plausibly recognized as Ca‐ and Ba‐containing particles. In a simple model based on demineralization data, lateral diffusion of Ca²⁺ between adjacent domains containing high‐ and low‐area Ca‐rich grains is described by exponential concentration gradients. These gradients may generate appreciable electromotive forces, which may enhance electrochemically the local tissue demineralization. Similar effects are to be expected in the protective action of F^? ions released from microgranules of YbF₃ and of Ba fluoroaluminosilicate glass. Copyright © 2010 John Wiley & Sons, Ltd.     

X‐Treme beamline at SLS: X‐ray magnetic circular and linear dichroism at high field and low temperature

X‐Treme is a soft X‐ray beamline recently built in the Swiss Light Source at the Paul Scherrer Institut in collaboration with École Polytechnique Fédérale de Lausanne. The beamline is dedicated to polarization‐dependent X‐ray absorption spectroscopy at high magnetic fields and low temperature. The source is an elliptically polarizing undulator. The end‐station has a superconducting 7 T–2 T vector magnet, with sample temperature down to 2 K and is equipped with an in situ sample preparation system for surface science. The beamline commissioning measurements, which show a resolving power of 8000 and a maximum flux at the sample of 4.7 × 10¹² photons s^?1, are presented. Scientific examples showing X‐ray magnetic circular and X‐ray magnetic linear dichroism measurements are also presented.     

Soft‐X‐ray ARPES facility at the ADRESS beamline of the SLS: concepts,technical realisation and scientific applications

Soft‐X‐ray angle‐resolved photoelectron spectroscopy (ARPES) with photon energies around 1 keV combines the momentum space resolution with increasing probing depth. The concepts and technical realisation of the new soft‐X‐ray ARPES endstation at the ADRESS beamline of SLS are described. The experimental geometry of the endstation is characterized by grazing X‐ray incidence on the sample to increase the photoyield and vertical orientation of the measurement plane. The vacuum chambers adopt a radial layout allowing most efficient sample transfer. High accuracy of the angular resolution is ensured by alignment strategies focused on precise matching of the X‐ray beam and optical axis of the analyzer. The high photon flux of up to 10¹³ photons s^?1 (0.01% bandwidth)^?1 delivered by the beamline combined with the optimized experimental geometry break through the dramatic loss of the valence band photoexcitation cross section at soft‐X‐ray energies. ARPES images with energy resolution up to a few tens of meV are typically acquired on the time scale of minutes. A few application examples illustrate the power of our advanced soft‐X‐ray ARPES instrumentation to explore the electronic structure of bulk crystals with resolution in three‐dimensional momentum, access buried heterostructures and study elemental composition of the valence states using resonant excitation.     

Distribution of Pb and Zn in slices of human bone by synchrotron µ‐XRF

Synchrotron radiation‐induced micro x‐ray fluorescence analysis (µ‐XRF) at HASYLAB beamline L was used to determine the distribution of Pb and other trace elements in slices of human bone. Using a focused synchrotron x‐ray beam of about 15 µm in diameter it was found that Pb was mostly located at the outer border of the cortical bone in various samples. Ratios of Pb intensities of cortical and trabecular bone varied from 0.027 for hip head to 0.408 for proximal tibia. Additionally Ca, Zn and Sr distributions were simultaneously recorded. A remarkable association between Pb and Zn content could be observed. Copyright © 2004 John Wiley & Sons, Ltd.     

A setup for synchrotron‐radiation‐induced total reflection X‐ray fluorescence and X‐ray absorption near‐edge structure recently commissioned at BESSY II BAMline

An automatic sample changer chamber for total reflection X‐ray fluorescence (TXRF) and X‐ray absorption near‐edge structure (XANES) analysis in TXRF geometry was successfully set up at the BAMline at BESSY II. TXRF and TXRF‐XANES are valuable tools for elemental determination and speciation, especially where sample amounts are limited (<1 mg) and concentrations are low (ng ml^?1 to µg ml^?1). TXRF requires a well defined geometry regarding the reflecting surface of a sample carrier and the synchrotron beam. The newly installed chamber allows for reliable sample positioning, remote sample changing and evacuation of the fluorescence beam path. The chamber was successfully used showing accurate determination of elemental amounts in the certified reference material NIST water 1640. Low limits of detection of less than 100 fg absolute (10 pg ml^?1) for Ni were found. TXRF‐XANES on different Re species was applied. An unknown species of Re was found to be Re in the +7 oxidation state.     

Implementation of ultrafast X‐ray diffraction at the 1W2B wiggler beamline of Beijing Synchrotron Radiation Facility

The implementation of a laser pump/X‐ray probe scheme for performing picosecond‐resolution X‐ray diffraction at the 1W2B wiggler beamline at Beijing Synchrotron Radiation Facility is reported. With the hybrid fill pattern in top‐up mode, a pixel array X‐ray detector was optimized to gate out the signal from the singlet bunch with interval 85 ns from the bunch train. The singlet pulse intensity is ～2.5 × 10⁶ photons pulse^?1 at 10 keV. The laser pulse is synchronized to this singlet bunch at a 1 kHz repetition rate. A polycapillary X‐ray lens was used for secondary focusing to obtain a 72 µm (FWHM) X‐ray spot. Transient photo‐induced strain in BiFeO₃ film was observed at a ～150 ps time resolution for demonstration.     

Fast‐scanning high‐flux microprobe for biological X‐ray fluorescence microscopy and microXAS

There is a growing interest in the biomedical community in obtaining information concerning the distribution and local chemical environment of metals in tissues and cells. Recently, biological X‐ray fluorescence microscopy (XFM) has emerged as the tool of choice to address these questions. A fast‐scanning high‐flux X‐ray microprobe, built around a recently commissioned pair of 200 mm‐long Rh‐coated silicon Kirkpatrick–Baez mirrors, has been constructed at BioCAT beamline 18ID at the Advanced Photon Source. The new optical system delivers a flux of 1.3 × 10¹² photons s^?1 into a minimum focal spot size of ～3–5 µm FWHM. A set of Si drift detectors and bent Laue crystal analyzers may be used in combination with standard ionization chambers for X‐ray fluorescence measurements. BioCAT's scanning software allows fast continuous scans to be performed while acquiring and storing full multichannel analyzer spectra per pixel on‐the‐fly with minimal overhead time (<20 ms per pixel). Together, the high‐flux X‐ray microbeam and the rapid‐scanning capabilities of the BioCAT beamline allow the collection of XFM and micro X‐ray absorption spectroscopy (microXAS) measurements from as many as 48 tissue sections per day. This paper reports the commissioning results of the new instrument with representative XFM and microXAS results from tissue samples.     

Simultaneous small‐ and wide‐angle scattering at high X‐ray energies

Combined small‐ and wide‐angle X‐ray scattering (SAXS/WAXS) is a powerful technique for the study of materials at length scales ranging from atomic/molecular sizes (a few angstroms) to the mesoscopic regime (～1 nm to ～1 µm). A set‐up to apply this technique at high X‐ray energies (E > 50 keV) has been developed. Hard X‐rays permit the execution of at least three classes of investigations that are significantly more difficult to perform at standard X‐ray energies (8–20 keV): (i) in situ strain analysis revealing anisotropic strain behaviour both at the atomic (WAXS) as well as at the mesoscopic (SAXS) length scales, (ii) acquisition of WAXS patterns to very large q (>20 Å^?1) thus allowing atomic pair distribution function analysis (SAXS/PDF) of micro‐ and nano‐structured materials, and (iii) utilization of complex sample environments involving thick X‐ray windows and/or samples that can be penetrated only by high‐energy X‐rays. Using the reported set‐up a time resolution of approximately two seconds was demonstrated. It is planned to further improve this time resolution in the near future.     

Multivariate calibrations for the SR‐TXRF determination of trace concentrations of lead and arsenic in the presence of bromine

A synchrotron radiation source and total reflection x‐ray fluorescence (SR‐TXRF) spectrometry were used for the determination of lead and arsenic in aqueous samples. To overcome the serious spectral interference between the two species and the overlap of another interfering element (bromine), a partial least‐squares regression (PLSR) method was used. The calibration models PLSR2 and PLSR1 were based on the x‐ray fluorescence emission signals (9.550–13.663 keV) for a set of 26 different mixtures containing the elements of interest, lead and arsenic, as well as bromine. The results obtained by PLSR1 and PLSR2 were compared with those obtained by the conventional univariate methodology. In the latter case, the areas of the secondary emission lines (Lβ for lead and Kβ for arsenic) were used to elaborate the analytical curves. The capacity of all optimized models was verified using five synthetic samples (external validation). Subsequently the best model was used to determine lead and arsenic recovery capacities when these metals are retained on two ion‐exchange resins (Dowex 50‐X8 and Dowex 1‐X8). The best multivariate model (PLSR1) allowed the determination of lead and arsenic with root mean square errors of prediction (RMSEPs) of 0.03 and 0.24 mg l^?1, respectively. The reduction of this parameter, with respect to the values obtained by conventional univariate methodology (0.26–0.03 mg l^?1 for lead and 0.30–0.24 mg l^?1 for arsenic), indicates that the proposed multivariate methodology really overcomes the problems associated with spectral interferences and minimizes the influence of an interfering agent (bromine). Copyright © 2005 John Wiley & Sons, Ltd.     

Pixelated transmission‐mode diamond X‐ray detector

Fabrication and testing of a prototype transmission‐mode pixelated diamond X‐ray detector (pitch size 60–100 µm), designed to simultaneously measure the flux, position and morphology of an X‐ray beam in real time, are described. The pixel density is achieved by lithographically patterning vertical stripes on the front and horizontal stripes on the back of an electronic‐grade chemical vapor deposition single‐crystal diamond. The bias is rotated through the back horizontal stripes and the current is read out on the front vertical stripes at a rate of ～1 kHz, which leads to an image sampling rate of ～30 Hz. This novel signal readout scheme was tested at beamline X28C at the National Synchrotron Light Source (white beam, 5–15 keV) and at beamline G3 at the Cornell High Energy Synchrotron Source (monochromatic beam, 11.3 keV) with incident beam flux ranges from 1.8 × 10^?2 to 90 W mm^?2. Test results show that the novel detector provides precise beam position (positional noise within 1%) and morphology information (error within 2%), with an additional software‐controlled single channel mode providing accurate flux measurement (fluctuation within 1%).