X-ray Fluorescence Elemental Mapping Research Articles

First record of carbonates with spherulites and cone-in-cone structures from the Precambrian of Arctic Norway, and their palaeoenvironmental significance

We report for the first time carbonates from the upper Ediacaran sedimentary succession of Finnmark, Arctic Norway. Carbonates occur as calcareous siliciclastic beds, lenses, and concretions, some with calcite spherulites and cone-in-cone (CIC) calcite, in a mudrock to fine-grained sandstone succession from approximately 3 m to 26 m above the base of the 2nd cycle of the Manndrapselva Member of the Stáhpogieddi Formation (Vestertana Group). They occur c. 40 m below the Ediacaran–Cambrian boundary, which is well defined by trace fossils. Thin-section petrography and scanning micro X-ray fluorescence elemental mapping reveal a layered composition of the calcareous sedimentary rocks. In some of those, well-developed nested cones of CIC calcite form the outer layer. Thin clay coatings outline individual cones. The inner layers are composed of (1) carbonate with calcite spherulites (grainstone) and (2) thinly laminated fine-grained calcareous siliciclastics (mudstone and wackestone) indicated by elevated concentrations of Al, Si, Fe, and Ti. The inner siliciclastic layers contain framboidal pyrite and probably organic matter. Formation of calcite spherulites took place probably at the sediment–water interface either in a coastal littoral environment or in situ in the sublittoral zone under high alkaline conditions whereas CIC calcite formed during burial diagenesis and clearly in pre-Caledonian time before metamorphism and cleavage formation. This new record of carbonates with calcite spherulites and CIC structures from the Ediacaran of Arctic Norway adds to their rare occurrences in the geological record.

Chemical Processing of an Early Salt Print Photograph Revealed with X-ray Fluorescence Elemental Mapping

Chemical Processing of an Early Salt Print Photograph Revealed with X-ray Fluorescence Elemental Mapping

Distribution and speciation of rare earth elements in coal combustion by-products via synchrotron microscopy and spectroscopy

Rare earth element (REE) binding environments and associated mineral phases in coal and coal combustion byproducts (CCBs) are not well understood. Advanced characterization of REEs' binding environments before, during, and after production can be vital in establishing an economically viable recovery method for REEs from these materials. This study characterized different REE distributions, cerium (Ce) oxidation states, and Ce binding environments in 11 CCBs collected from various locales via X-ray fluorescence (XRF) elemental mapping and X-ray absorption near edge structure (XANES) at Stanford Synchrotron Radiation Lightsource (SSRL). Bulk Ce LIII edge XANES identified Ce(III) (>85%) as the predominant Ce oxidation state in all studied samples. Ce speciation and XRF elemental map analyses further reveal the REEs in studied samples can be (1) dispersed throughout the aluminosilicate glass phase, (2) as micro-particles in large glass grain, or (3) as independent trace phases in studied samples. Both fly ash and bottom ash contain mainly Ce(III) micro-hotspots (<40 μm), co-localization with a range of elements, including, but not limited to: P, S, Ca, Ti, and Mn. At microscale, Ce can change from Ce(III) to mixture of Ce(III) and Ce(IV) and to 100% Ce(IV) oxide, revealing potential REE-phase decomposition and oxidation in coal and coal combustion process. Our study also observed intraparticle and interparticle distribution difference between light REEs and heavy REEs. The synchrotron-based characterization confirmed the presence of these trace, previously only theorized, phases during the combustion process and ultimately may inform the simplification of separation and extraction processes for REE from different CCBs.

Evidence of lateral thermomechanical erosion of basalt by Fe-Ni-Cu sulfide melt at Kambalda, Western Australia

Abstract The Fe-Ni-Cu sulfide ores at Kambalda, Western Australia, are interpreted to be the result of thermomechanical erosion of underlying rocks by the host komatiite lava flows. However, there is a long-standing argument about the extent of the erosion process, and the degree to which the linear embayments that host the ores were eroded by lava as opposed to formed by tectonic processes. This controversy has fundamental implications for the origin of magmatic sulfide ore, as well as for sinuous rilles on terrestrial planets. The controversy at Kambalda hinges on pinchout features, where sulfide ore at the edges of embayments penetrates laterally into footwall rocks. The most recently published studies of these features interpret them as forming by thrusting of basalts over sulfide-komatiite contacts along the margins of tectonic embayments. Field evidence and X-ray fluorescence element mapping on underground exposures in the Moran deposit demonstrate that sulfide liquid melted its way both downward and laterally into basalt, generating complex plumose melt layers, melt emulsions, and hybridized chromite-decorated contacts. These observations confirm an origin for the pinchouts by thermomechanical erosion, driven by the high temperature, high density, and low viscosity of the sulfide melt. They also provide some intriguing insights into the nature of interactions between sulfide melt and melting silicate rocks in magmatic Ni-Cu-platinum group element sulfide ore deposits in general.

Performance of asymmetric supercapacitor using CoCr-layered double hydroxide and reduced graphene-oxide

Cobalt chromium-layered double hydroxides (CoCr-LDHs) were electrodeposited on to carbon paper by potentiostatic method from the respective cobalt and chromium ion sources. The electrodeposited CoCr-LDHs were characterized by x-ray diffraction (XRD), Fourier transferred infrared (FT-IR) spectroscopy, scanning electron microscope (SEM), energy-dispersive x-ray analysis (EDX) and x-ray fluorescence (XRF) elemental mapping. The XRD and IR data confirmed that the deposits were CoCr-LDH with carbonate and nitrate ions in the basal space. The SEM observations confirmed that the CoCr-LDH surface had distinct morphology consisting of aggregate size of about 100 nm. For the first time, the supercapacitor characteristics of the CoCr-LDHs were assessed in three-electrode configuration in 1 M KOH or two-electrode (asymmetric capacitor device with reduced graphene-oxide (RGO)). It turned out that the asymmetric capacitor consisted of the CoCr-LDH and the RGO exhibited higher energy density with excellent power density. The higher energy density and power density of the asymmetric capacitor device is believed to be due to the unique LDH morphology in addition to the Faradaic and non-Faradaic contributions. It was demonstrated that the two asymmetric capacitor devices connected in series could light an LED bulb.

A Hidden Portrait by Edgar Degas.

The preservation and understanding of cultural heritage depends increasingly on in-depth chemical studies. Rapid technological advances are forging connections between scientists and arts communities, enabling revolutionary new techniques for non-invasive technical study of culturally significant, highly prized artworks. We have applied a non-invasive, rapid, high definition X-ray fluorescence (XRF) elemental mapping technique to a French Impressionist painting using a synchrotron radiation source, and show how this technology can advance scholarly art interpretation and preservation. We have obtained detailed technical understanding of a painting which could not be resolved by conventional techniques. Here we show 31.6 megapixel scanning XRF derived elemental maps and report a novel image processing methodology utilising these maps to produce a false colour representation of a “hidden” portrait by Edgar Degas. This work provides a cohesive methodology for both imaging and understanding the chemical composition of artworks, and enables scholarly understandings of cultural heritage, many of which have eluded conventional technologies. We anticipate that the outcome from this work will encourage the reassessment of some of the world’s great art treasures.

Bioturbating animals control the mobility of redox-sensitive trace elements in organic-rich mudstone

Bioturbating animals modify the original mineralogy, porosity, organic content, and fabric of mud, thus affecting the burial diagenetic pathways of potential hydrocarbon source, seal, and reservoir rocks. High-sensitivity, synchrotron rapid scanning X-ray fluorescence elemental mapping reveals that producers of phycosiphoniform burrows systematically partition redox-sensitive trace elements (i.e., Fe, V, Cr, Mn, Co, Ni, Cu, and As) in fine-grained siliciclastic rocks. Systematic differences in organic carbon content (total organic carbon >1.5 wt%) and quality (Δ13Corg~0.6‰) are measured between the burrow core and host sediment. The relative enrichment of redox-sensitive elements in the burrow core does not correlate with significant neo-formation of early diagenetic pyrite (via trace metal pyritization), but is best explained by physical concentration of clay- and silt-sized components. A measured loss (~–15%) of the large-ionic-radius elements Sr and Ba from both burrow halo and core is most likely associated with the release of Sr and Ba to pore waters during biological (in vivo) weathering of silt- to clay-sized lithic components and feldspar. In conclusion, this newly documented effect has significant potential to inform the interpretation of geochemical proxy and rock property data, particularly from shales, where elemental analyses are commonly employed to predict reservoir quality and support paleoenvironmental analysis.

Vivianite is a major sink for phosphorus in methanogenic coastal surface sediments

Studies of authigenic phosphorus (P) minerals in marine sediments typically focus on authigenic carbonate fluorapatite, which is considered to be the major sink for P in marine sediments and can easily be semi-quantitatively extracted with the SEDEX sequential extraction method. The role of other potentially important authigenic P phases, such as the reduced iron (Fe) phosphate mineral vivianite (Fe(II)3(PO4)*8H2O) has so far largely been ignored in marine systems. This is, in part, likely due to the fact that the SEDEX method does not distinguish between vivianite and P associated with Fe-oxides. Here, we show that vivianite can be quantified in marine sediments by combining the SEDEX method with microscopic and spectroscopic techniques such as micro X-ray fluorescence (μXRF) elemental mapping of resin-embedded sediments, as well as scanning electron microscope–energy dispersive spectroscopy (SEM–EDS) and powder X-ray diffraction (XRD). We further demonstrate that resin embedding of vertically intact sediment sub-cores enables the use of synchrotron-based microanalysis (X-ray absorption near-edge structure (XANES) spectroscopy) to differentiate between different P burial phases in aquatic sediments. Our results reveal that vivianite represents a major burial sink for P below a shallow sulfate/methane transition zone in Bothnian Sea sediments, accounting for 40–50% of total P burial. We further show that anaerobic oxidation of methane (AOM) drives a sink-switching from Fe-oxide bound P to vivianite by driving the release of both phosphate (AOM with sulfate and Fe-oxides) and ferrous Fe (AOM with Fe-oxides) to the pore water allowing supersaturation with respect to vivianite to be reached. The vivianite in the sediment contains significant amounts of manganese (∼4–8wt.%), similar to vivianite obtained from freshwater sediments. Our results indicate that methane dynamics play a key role in providing conditions that allow for vivianite authigenesis in coastal surface sediments. We suggest that vivianite may act as an important burial sink for P in brackish coastal environments worldwide.

Mapping Henry: Synchrotron-sourced X-ray fluorescence mapping and ultra-high-definition scanning of an early Tudor portrait of Henry VIII

A portrait of Henry VIII on oak panel c. 1535 has recently undergone technical examination to inform questions regarding authorship and the painting’s relationship to a group of similar works in the collections of the National Portrait Gallery, London, and the Society of Antiquaries. Due to previous conservation treatments of the painting, the conventional transmission X-radiograph image was difficult to interpret. As a result, the painting underwent high-definition X-ray fluorescence (XRF) elemental mapping on the X-ray fluorescence microscopy beamline of the Australian Synchrotron. Scans were conducted at 12.6 and 18.5 keV, below and above the lead (Pb) L edges, respectively. Typical scan parameters were 120 μm pixel size at 7 ms dwell time, with the largest scan covering an area 545 × 287 mm2 collected in 23 h (10.8 MP). XRF mapping of the panel has guided the conservation treatment of the painting and the revelation of previously obscured features. It has also provided insight into the process of making of the painting. The informative and detailed elemental maps, alongside ultra-high-definition scans of the painting undertaken before and after varnish and over-paint removal, have assisted in comparison of the finely painted details with the London paintings. The resolution offered by the combination of imaging techniques identifies pigment distribution at an extremely fine scale, enabling a new understanding of the artist’s paint application.

X-ray nano-diffraction study of Sr intermetallic phase during solidification of Al-Si hypoeutectic alloy

The evolution of strontium (Sr) containing intermetallic phase in the eutectic reaction of Sr-modified Al-Si hypoeutectic alloy was studied with high energy synchrotron beam source for nano-diffraction experiments and x-ray fluorescence elemental mapping. Contrary to popular belief, Sr does not seem to interfere with the Twin Plane Re-entrant Edge (TPRE) growth mechanism of eutectic Si, but evolves as the Al2Si2Sr phase during the eutectic reaction at the boundary between the eutectic Si and Al grains.

Leaf metallome preserved over 50 million years.

Large-scale Synchrotron Rapid Scanning X-ray Fluorescence (SRS-XRF) elemental mapping and X-ray absorption spectroscopy are applied here to fossil leaf material from the 50 Mya Green River Formation (USA) in order to improve our understanding of the chemistry of fossilized plant remains. SRS-XRF of fossilized animals has previously shown that bioaccumulated trace metals and sulfur compounds may be preserved in their original distributions and these elements can also act as biomarkers for specific biosynthetic pathways. Similar spatially resolved chemical data for fossilized plants is sparsely represented in the literature despite the multitude of other chemical studies performed. Here, synchrotron data from multiple specimens consistently show that fossil leaves possess chemical inventories consisting of organometallic and organosulfur compounds that: (1) map discretely within the fossils, (2) resolve fine scale biological structures, and (3) are distinct from embedding sedimentary matrices. Additionally, the chemical distributions in fossil leaves are directly comparable to those of extant leaves. This evidence strongly suggests that a significant fraction of the chemical inventory of the examined fossil leaf material is derived from the living organisms and that original bioaccumulated elements have been preserved in situ for 50 million years. Chemical information of this kind has so far been unknown for fossilized plants and could for the first time allow the metallome of extinct flora to be studied.

Microscale analysis of metal uptake by argillaceous rocks using positive matrix factorization of microscopic X-ray fluorescence elemental maps

Argillaceous rocks are considered in most European countries as suitable host rock formations for the deep geological disposal of high-level radioactive waste (HLW). The most important chemical characteristic in this respect is their generally strong radionuclide retention property due to the high sorption capacity. Consequently, the physico-chemical parameters of these processes have to be studied in great detail. Synchrotron radiation microscopic X-ray fluorescence (SR μ-XRF) has sufficient sensitivity to study these processes on the microscale without the necessity of the application of radioactive substances. The present study focuses on the interaction between the escaped ions and the host-rock surrounding the planned HLW repository. SR μ-XRF measurements were performed on thin sections subjected to sorption experiments using 5μm spatial resolution. Inactive Cs(I), Ni(II), Nd(III) and natural U(VI) were selected for the experiments chemically representing key radionuclides. The thin sections were prepared on high-purity silicon wafers from geochemically characterized cores of Boda Claystone Formation, Hungary. Samples were subjected to 72-hour sorption experiments with one ion of interest added. The μ-XRF elemental maps taken usually on several thousand pixels indicate a correlation of Cs and Ni with Fe- and K-rich regions suggesting that these elements are predominantly taken up by clay-rich phases. U and Nd was found to be bound not only to the clayey matrix, but the cavity filling minerals also played important role in the uptake. Multivariate methods were found to be efficient tools for extracting information from the elemental distribution maps even when the clayey matrix and fracture infilling regions were examined in the same measured area. By using positive matrix factorization as a new approach the factors with higher sorption capacity could be identified and with additional mineralogical information the uptake capacity of the different mineral phases could be quantified. The results were compared with cluster analysis when the regions dominated by different mineral phases are segmented. The multivariate approach based on μ-XRF to identify the minerals was validated using microscopic X-ray diffraction.

In Situ Spectroelectrochemistry at Free-Standing Liquid–Liquid Interfaces: UV–vis Spectroscopy, Microfocus X-ray Absorption Spectroscopy, and Fluorescence Imaging

A windowless electrochemical cell for the spectroscopic investigation of the liquid–liquid interface, using a dual droplet configuration, has been designed. The setup permits in situ probing of the bulk solutions and the interfacial region by fiber-optic UV–vis spectroscopy, microfocus X-ray fluorescence (XRF) elemental mapping, and microfocus X-ray absorption near-edge structure (μXANES) spectroscopy. The electrodeposition of Au, induced by ion transfer of the tetrachloroaurate complex from a halogenated solvent (containing a weak reducing agent) to the aqueous phase, has been monitored by a combination of the three techniques. The reaction can be followed in situ by UV–vis spectroscopy by detecting the oxidized form of the reducing agent. Voltammetric evidence suggests the formation of interfacial Au(I) species, whereas μXANES detect the presence of metallic Au(0).

Strontium Substitution for Calcium in Lithogenesis

Strontium has chemical similarity to calcium, which enables the replacement of calcium by strontium in biomineralization processes. Incorporating strontium into human bone and teeth has been studied extensively but little research has been performed of the incorporation of strontium into urinary calculi. We used synchrotron based x-ray fluorescence and x-ray absorption techniques to examine the presence of strontium in different types of human kidney stones. Multiple unique human stone samples were obtained via consecutive percutaneous nephrolithotomies/ureteroscopies. A portion of each stone was sent for standard laboratory analysis and a portion was retained for x-ray fluorescence and x-ray absorption measurements. X-ray fluorescence and x-ray absorption measurements determined the presence, spatial distribution and speciation of strontium in each stone sample. Traditional kidney stone analyses identified calcium oxalate, calcium phosphate, uric acid and cystine stones. X-ray fluorescence measurements identified strontium in all stone types except pure cystine. X-ray fluorescence elemental mapping of the samples revealed co-localization of calcium and strontium. X-ray absorption measurements of the calcium phosphate stone showed strontium predominately present as strontium apatite. Advanced x-ray fluorescence imaging identified strontium in all calcium based stones, present as strontium apatite. This finding may be critical since apatite is thought to be the initial nidus for calcium stone formation. Strontium is not identified by standard laboratory stone analyses. Its substitution for calcium can be reliably identified in stones from multiple calcium based stone formers, which may offer opportunities to gain insight into early events in lithogenesis.

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LOCALIZATION OF IRON WITHIN CENTRIC DIATOMS OF THE GENUS THALASSIOSIRA(1).

The cellular iron (Fe) quota of centric diatoms has been shown to vary in response to the ambient dissolved Fe concentration; however, it is not known how centric diatoms store excess intracellular Fe. Here, we use synchrotron X-ray fluorescence (SXRF) element mapping to identify Fe storage features in cells of Thalassiosira pseudonana Hasle et Heimdal and Thalassiosira weissflogii G. A. Fryxell et Hasle grown at low and high Fe concentrations. Localized intracellular Fe storage features, defined as anomalously high Fe concentrations in regions of relatively low phosphorus (P), sulfur (S), silicon (Si), and zinc (Zn), were twice as common in T. weissflogii cells grown at high Fe compared to low-Fe cells. Cellular Fe quotas of this strain increased 2.9-fold, the spatial extent of the features increased 4.6-fold, and the Fe content of the features increased 14-fold under high-Fe conditions, consistent with a vacuole storage mechanism. The element stoichiometry of the Fe features is consistent with polyphosphate-bound Fe as a potential vacuolar Fe storage pool. Iron quotas increased 2.5-fold in T. pseudonana grown at high Fe, but storage features contained only 2-fold more Fe and did not increase in size compared to low-Fe cells. The differences in Fe storage observed between T. pseudonana and T. weissflogii may have been due to differences in the growth states of the cultures.

2082 STRONTIUM SUBSTITUTION FOR CALCIUM IN LITHOGENESIS

You have accessJournal of UrologyStone Disease: Basic Research I1 Apr 20122082 STRONTIUM SUBSTITUTION FOR CALCIUM IN LITHOGENESIS Sarah D. Blaschko, MD Lawrence Flechner, MD Gyorgy Snell, PhD Thomas Chi, MD Joe Miller, MD Sirine Fakra, andMS Marshall L. StollerMD Sarah D. BlaschkoSarah D. Blaschko San Francisco, CA More articles by this author , Lawrence FlechnerLawrence Flechner San Francisco, CA More articles by this author , Gyorgy SnellGyorgy Snell Berkeley, CA More articles by this author , Thomas ChiThomas Chi San Francisco, CA More articles by this author , Joe MillerJoe Miller San Francisco, CA More articles by this author , Sirine FakraSirine Fakra Berkeley, CA More articles by this author , and Marshall L. StollerMarshall L. Stoller San Francisco, CA More articles by this author View All Author Informationhttps://doi.org/10.1016/j.juro.2012.02.2248AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookTwitterLinked InEmail INTRODUCTION AND OBJECTIVES Strontium has two available valence electrons for chemical bonding and is positioned in the same column of the periodic table as calcium. This chemical similarity enables the replacement of calcium by strontium in biological processes. Strontium has long been used as a substitute for calcium when testing calcium absorption in the gut and calcium filtration by the kidney and exists as four stable isotopes. Ratios of these isotopes have been used to identify the origins of plants, animals, and soil. Incorporation of strontium into human bone and teeth has been studied extensively, however little research has been performed on the incorporation of strontium into urinary calculi. We utilized synchrotron based X-ray fluorescence (XRF) and X-ray absorption (XAS) techniques to examine the presence of strontium in different types of human kidney stones. We postulate that the presence of strontium in urolithiasis may be utilized to help better understand early calcium-based stone pathogenesis. METHODS Multiple unique human stone samples were obtained via consecutive percutaneous nephrolithotomies/ureteroscopies and a portion was sent for standard laboratory analysis with Fourier Transform Infrared Spectroscopy (FTIR). XRF and XAS measurements were carried out at the Advanced Light Source synchrotron radiation facility at the Lawrence Berkeley National Laboratory to examine the presence, spatial distribution and speciation of strontium in each stone sample. RESULTS Traditional kidney stone analyses identified calcium oxalate, calcium phosphate, uric acid, and cystine stones. XRF measurements identified strontium in all stone types except for pure cystine. XRF elemental mapping of the samples revealed co-localization of calcium and strontium. XAS measurements of the calcium phosphate stone showed that strontium is predominately present as strontium apatite. CONCLUSIONS Advanced X-ray fluorescence methods identified strontium in all calcium based stones and is present as strontium apatite. This finding may be critical as apatite is often thought to be the initial nidus for calcium stone formation. Strontium is overlooked with standard laboratory stone analyses; substitution for calcium can be reliably identified in stones from multiple calcium-based stone formers with different stone compositions and offers insight into early events in lithogenesis. © 2012 by American Urological Association Education and Research, Inc.FiguresReferencesRelatedDetails Volume 187Issue 4SApril 2012Page: e839 Peer Review Report Advertisement Copyright & Permissions© 2012 by American Urological Association Education and Research, Inc.MetricsAuthor Information Sarah D. Blaschko San Francisco, CA More articles by this author Lawrence Flechner San Francisco, CA More articles by this author Gyorgy Snell Berkeley, CA More articles by this author Thomas Chi San Francisco, CA More articles by this author Joe Miller San Francisco, CA More articles by this author Sirine Fakra Berkeley, CA More articles by this author Marshall L. Stoller San Francisco, CA More articles by this author Expand All Advertisement Advertisement PDF downloadLoading ...

High-Definition X-ray Fluorescence Elemental Mapping of Paintings

A historical self-portrait painted by Sir Arthur Streeton (1867-1943) has been studied with fast-scanning X-ray fluorescence microscopy using synchrotron radiation. One of the technique's unique strengths is the ability to reveal metal distributions in the pigments of underlying brushstrokes, thus providing information critical to the interpretation of a painting. We have applied the nondestructive technique with the event-mode Maia X-ray detector, which has the capability to record elemental maps at megapixels per hour with the full X-ray fluorescence spectrum collected per pixel. The painting poses a difficult challenge to conventional X-ray analysis, because it was completely obscured with heavy brushstrokes of highly X-ray absorptive lead white paint (2PbCO(3)·Pb(OH)(2)) by the artist, making it an excellent candidate for the application of the synchrotron-based technique. The 25 megapixel elemental maps were successfully observed through the lead white paint across the 200 × 300 mm(2) scan area. The sweeping brushstrokes of the lead white overpaint contributed significant detrimental structure to the elemental maps. A corrective procedure was devised to enhance the visualization of the elemental maps by using the elastic X-ray scatter as a proxy for the lead white overpaint. We foresee the technique applied to the most demanding of culturally significant artworks where conventional analytical methods are inadequate.

Reverse engineering the ancient ceramic technology based on X-ray fluorescence spectromicroscopy

We present results of X-ray fluorescence (XRF) microprobe analyses of ancient ceramic cross-sections aiming at deciphering the different firing protocols used for their production. Micro-focused XRF elemental mapping, Fe chemical mapping and Fe K-edge X-ray absorption near edge structure spectroscopy were performed on pre-sigillata ceramics from southern Gaul, and terra Sigillata vessels from Italy and southern Gaul. Pieces from the different workshops and regions showed significant difference in the starting clay material, clay conditioning and kiln firing condition. By contrast, sherds from the same workshop exhibited more subtle differences and possible misfirings. Understanding the precise firing conditions and protocols would allow recreation of kilns for various productions. Furthermore, evolution and modification of kiln design would shed some light on how ancient potters devised solutions to diverse technological problems they encountered.

Selenium accumulation, distribution, and speciation in spineless prickly pear cactus: a drought- and salt-tolerant, selenium-enriched nutraceutical fruit crop for biofortified foods.

The organ-specific accumulation, spatial distribution, and chemical speciation of selenium (Se) were previously unknown for any species of cactus. We investigated Se in Opuntia ficus-indica using inductively coupled plasma mass spectrometry, microfocused x-ray fluorescence elemental and chemical mapping (μXRF), Se K-edge x-ray absorption near-edge structure (XANES) spectroscopy, and liquid chromatography-mass spectrometry (LC-MS). μXRF showed Se concentrated inside small conic, vestigial leaves (cladode tips), the cladode vasculature, and the seed embryos. Se K-edge XANES demonstrated that approximately 96% of total Se in cladode, fruit juice, fruit pulp, and seed is carbon-Se-carbon (C-Se-C). Micro and bulk XANES analysis showed that cladode tips contained both selenate and C-Se-C forms. Inductively coupled plasma mass spectrometry quantification of Se in high-performance liquid chromatography fractions followed by LC-MS structural identification showed selenocystathionine-to-selenomethionine (SeMet) ratios of 75:25, 71:29, and 32:68, respectively in cladode, fruit, and seed. Enzymatic digestions and subsequent analysis confirmed that Se was mainly present in a "free" nonproteinaceous form inside cladode and fruit, while in the seed, Se was incorporated into proteins associated with lipids. μXRF chemical mapping illuminated the specific location of Se reduction and assimilation from selenate accumulated in the cladode tips into the two LC-MS-identified C-Se-C forms before they were transported into the cladode mesophyll. We conclude that Opuntia is a secondary Se-accumulating plant whose fruit and cladode contain mostly free selenocystathionine and SeMet, while seeds contain mainly SeMet in protein. When eaten, the organic Se forms in Opuntia fruit, cladode, and seed may improve health, increase Se mineral nutrition, and help prevent multiple human cancers.