Akiko Hokura

Electrochemically Reversible Sodium Intercalation of Layered NaNi0.5Mn0.5O2 and NaCrO2

Electrochemical activities of NaNi0.5Mn0.5O2 and NaCrO2, having the analogous layered structure to LiCoO2, were investigated in 1 mol dm-3 NaClO4 propylene carbonate at room temperature. Almost all sodium ions were extracted from the NaNi0.5Mn0.5O2 and NaCrO2 electrodes by galvanostatic oxidation to 4.5 V accompanied with several phase transitions. Layered NaNi0.5Mn0.5O2 electrode showed a highly reversible capacity of 185 mAh g-1 as positive electrode in Na cell in the potential region between 2.5 and 4.5 V versus Na. A NaCrO2 electrode was hardly electroactive after oxidation up to 4.5 V. When galvanostatic cycling was carried in the limited potential domain between 2 and 3.5 V, both electrodes showed discharge capacities of 100 - 120 mAh g-1 with satisfactory capacity retention. Layered LiCrO2 (R-3m) and NaCrO2 (R-3m) possess the quite similar crystal structures and the same transition metal, nevertheless they were inactive and active in Li and Na cells, respectively.

In vivo analysis of metal distribution and expression of metal transporters in rice seed during germination process by microarray and X-ray Fluorescence Imaging of Fe, Zn, Mn, and Cu

To investigate the flow of the metal nutrients iron (Fe), zinc (Zn), manganese (Mn), and copper (Cu) during rice seed germination, we performed microarray analysis to examine the expression of genes involved in metal transport. Many kinds of metal transporter genes were strongly expressed and their expression levels changed during rice seed germination. We found that metal transporter genes such as ZIP family has tendency to decrease in their expressions during seed germination. Furthermore, imaging of the distribution of elements (Fe, Mn, Zn, and Cu) was carried out using Synchrotron-based X-ray microfluorescence at the Super Photon ring-8 GeV (SPring-8) facility. The change in the distribution of each element in the seeds following germination was observed by in vivo monitoring. Iron, Mn, Zn, and Cu accumulated in the endosperm and embryos of rice seeds, and their distribution changed during rice seed germination. The change in the patterns of mineral localization during germination was different among the elements observed.

Micro X-ray fluorescence imaging and micro X-ray absorption spectroscopy of cadmium hyper-accumulating plant, Arabidopsis halleri ssp. gemmifera, using high-energy synchrotron radiation

Monochromatic high-energy X-rays (37 keV) focused into a microbeam (3.8 × 1.3 μm2) with a Kirkpatrick-Baez mirror allows us for the first time to reveal the striking sub-cellular distribution and the chemical form of cadmium in the cadmium hyperaccumulating plant, Arabidopsis halleri ssp. gemmifera, by detecting the Cd Kα line. Micro X-ray fluorescence analysis (μ-XRF) and micro X-ray absorption near-edge structure analysis (μ-XANES) were used for the nondestructive analysis of the Cd distribution and chemical form of Cd at a cellular level in the plant in order to investigate the Cd accumulation mechanism. It was clearly observed by two-dimensional μ-XRF imaging that Cd was highly accumulated in a part of the trichomes, epidermal hairs existing on the surface of the leaves. The bases of the trichomes contained Cd, Zn and Mn at high concentrations and their distribution patterns were similar to each other. These elements were located near the surface of the trichome in the form of a ring. The μ-XANES analysis revealed that the majority of the Cd exists in the divalent state and bound to the O and/or N ligands. This study has demonstrated the potential of the Cd K-edge μ-XANES spectroscopy, which was applied here for the first time to plant samples.

Arsenic distribution and speciation in an arsenic hyperaccumulator fern by X-ray spectrometry utilizing a synchrotron radiation source

The arsenic distribution in the arsenic hyper-accumulating fern (Pteris vittata L.) was investigated using a synchrotron X-ray fluorescence microprobe. Fronds of various ages were subjected to XRF imaging analysis, and it was found that the arsenic distribution in the pinnae of fronds changed according to their stage of growth. The focused microbeam (3.5 × 5.5 μm2) produced by Kirkpatrick–Baez optics was applied to the fern in order to determine the elemental distribution in plant tissue and cell levels. The results indicated that high levels of arsenic accumulate at the base of sporangium with lamina of pinnae. Also, the fern was subjected to X-ray absorption near edge structure (XANES) analysis without any sample treatment to directly elucidate the arsenic oxidation state in fern. It was found that arsenic exists as the As(III) form in pinnae, and as a mixture of As(III) and As(V) in rachis, while As(V) is present in cultivated soil. These findings indicate that the fern uptakes arsenic as As(V) from soil and that the As(V) is then partially reduced to As(III) within the plant, with the arsenic finally accumulating as As(III) in a specific area of the pinna.

Characterization of Cadmium Accumulation in Willow as a Woody Metal Accumulator Using Synchrotron Radiation-Based X-Ray Microanalyses

Trees that accumulate metals are important plants for restoring contaminated soil because of their high biomass. We examined the cadmium (Cd) tolerance and growth rate of six willow (Salix) species common in Japan. To characterize in detail the localization of Cd and its ligands, synchrotron radiation-based micro X-ray fluorescence analysis was used. This revealed the accumulation of cadmium at the tips of the serrations in leaves, and the phellogen and/or the phelloderm under the stem surface. micro-X-ray absorption near edge structure spectra of Cd in all the accumulation sites were similar to that of the Cd ion coordinated by O ligands in S. gilgiana.

Determination of trace elements in soybean by X-ray fluorescence analysis and its application to identification of their production areas.

Trace elemental analysis of soybeans was performed using X-ray fluorescence (XRF) analysis in order to characterise the geographical origins of the beans. By optimising the measurement conditions of an energy-dispersive XRF spectrometer equipped with three-dimensional polarisation optics, determination of trace elements at the sub-μgg(-1) level in soybean samples was accomplished. Forty-six samples were analysed. Results showed that there were some differences between the trace element contents, reflecting a difference in their geographical origins. A statistical analysis showed that the concentrations of eight elements (Mg, P, Cl, K, Mn, Cu, Br, and Ba) are good parameters for constructing a discriminant function for geographical origin. In conclusion, we were able to accurately distinguish between domestic and imported soybeans. The present work demonstrates that XRF is useful as a rapid and simple tool for provenance analyses of agricultural products.

A KINETIC STUDY OF NICKEL ION EXTRACTION BY KELEX 100 AT THE LIQUID-LIQUID INTERFACE

ABSTRACT A study of the kinetics of nickel ion extraction by Kelex 100 (7-(4-ethyl-1-methyloctyl)8-hydroxyquinoline) is presented. A reaction scheme is proposed and the kinetics are shown to be controlled by the two parallel initial addition steps. The forward reaction rate constants are determined for these cases. The techniques used to measure the kinetics are, stopped flow where the organic ligand is solubilised in micelles and attenuated total internal reflection spectroscopy (ATR). The first is based on the kinetics at a non-ionic micelle interface and the second at a free aqueous-organic interface. Identical results for the kinetics were obtained from the two techniques when variations in the interfacial pKas of the Kelex 100 are considered due to variations in the dielectic constants of the two different interfaces investigated.

Development of Desolvation System for Single-cell Analysis Using Droplet Injection Inductively Coupled Plasma Atomic Emission Spectroscopy.

With a view to enhance the sensitivity of analytical instruments used in the measurement of trace elements contained in a single cell, we have now equipped the previously reported micro-droplet injection system (M-DIS) with a desolvation system. This modified M-DIS was coupled to inductively coupled plasma atomic emission spectroscopy (ICP-AES) and evaluated for its ability to measure trace elements. A flow rate of 100 mL/min for the additional gas and a measurement point -7.5 mm above the load coil (ALC) have been determined to be the optimal parameters for recording the emission intensity of the Ca(II) spectral lines. To evaluate the influence of the desolvation system, we recorded the emission intensities of the Ca(I), Ca(II), and H-β spectral lines with and without inclusion of the desolvation system. The emission intensity of the H-β spectral line reduces and the magnitude of the Ca(II)/Ca(I) emission intensity ratio increases four-fold with inclusion of the desolvation system. Finally, the elements Ca, Mg, and Fe present in a single cell of Pseudococcomyxa simplex are simultaneously determined by coupling the M-DIS equipped with the desolvation system to ICP-AES.

Radiocesium accumulation in Egeria densa, a submerged plant – possible mechanism of cesium absorption

Radioactive cesium (Cs) was discharged into the environment in the northeast region of Japan after destruction of the nuclear power station in March 2011. In this work, we study the uptake and accumulation of Cs in a freshly submerged vascular plant, Egeria densa (Brazilian waterweed, Hydrocharitaceae), to investigate the behavior of Cs in the aquatic ecosystem and to predict the movement of the radionuclide to remove this Cs from the environment. We collected plants, waters, and sediments that had been contaminated by radioactive fallout in Fukushima Prefecture in September 2012. The activities of 134Cs, 137Cs, and 40K were measured using a germanium semiconductor detector. We found that the endogenous radioactive Cs concentrations in plants were correlated with those in the sediments. To discuss the uptake mechanism of Cs, stable 133Cs was applied separately to shoots and roots in a two-compartment bath. The results showed that the environmental Cs transferred to both shoot and root parts in plants. To analyze the detailed localization of Cs in plants, synchrotron radiation-based micro X-ray fluorescence (SR-μ-XRF) analysis was performed for the plants cultivated in a hydroponic medium containing 133Cs. The two-dimensional metal distribution of leaves was determined by μ-XRF with approximately 0.7 μm X-ray beams. The distribution showed the predominant localization of Cs, K as well as several divalent metals in the cell wall or apoplastic regions, suggesting the possible absorption mechanism of Cs in the plants. We concluded that E. densa plays an important role in the deposition of radioactive Cs in fresh water.

Quantitative Analysis of Major and Minor Elements in Lead-free Solder Chip by LA-ICP-MS

A method was established for the quantitative analysis of the elements (Cu, Ag, Pb, and Sn) in solder samples by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), with Sn-based matrix matched standard solutions for defining the calibration curves. It was found that chloride-ion presented in commercially available Sn standard solution resulted in a precipitation of AgCl and caused the deterioration of the linearity of the calibration curve for Ag. Therefore, a laboratory-made chloride-free Sn solution was used to prepare Sn matrix matched standard solutions so as to ensure the stability of the elements including Ag. For the quantitative analysis of solder samples by LA-ICP-MS, the operating conditions of the LA instruments were set to obtain a fluence of over 12 J cm-2. This is mainly because of larger LA-induced elemental fractionations using a fluence of <10 J cm-2. The results for Ag, Cu, Pb, and Sn in a certified reference material (NMIJ CRM 8203-a) were close to, or in agreement with, the certified values, indicating that the present method was valid for the quantitative analysis of the elements in solder samples. In comparison to the certified values, relatively larger uncertainties were obtained for the analytical results by LA-ICP-MS, which could be attributed to the dependence on the homogeneity of the sample because the sample aliquots used for analysis were much smaller than those required for the traditional analytical procedures (i.e., sample quantity ratio of ca. 1:13000). Further improvement of the uncertainty might be obtained by using a larger sample quantity for the analysis by LA-ICP-MS so as to improve the representativeness of the sample.