Akiharu Hioki

Improved measurement results for the Avogadro constant using a 28Si-enriched crystal

New results are reported from an ongoing international research effort to accurately determine the Avogadro constant by counting the atoms in an isotopically enriched silicon crystal. The surfaces of two 28Si-enriched spheres were decontaminated and reworked in order to produce an outer surface without metal contamination and improved sphericity. New measurements were then made on these two reconditioned spheres using improved methods and apparatuses. When combined with other recently refined parameter measurements, the Avogadro constant derived from these new results has a value of

Speciation and monitoring test for inorganic arsenic in white rice flour.

N_A = 6.022 140 76(12) \times 10^{23}

Extraction techniques for arsenic species in rice flour and their speciation by HPLC-ICP-MS.

mol

Highly efficient single-cell analysis of microbial cells by time-resolved inductively coupled plasma mass spectrometry

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Erratum to: Preparation and certification of Hijiki reference material, NMIJ CRM 7405-a, from the edible marine algae hijiki (Hizikia fusiforme)

. The X-ray crystal density method has thus achieved the target relative standard uncertainty of

Investigation of iodine liberation process in redox titration of potassium iodate with sodium thiosulfate

2.0 \times 10^{-8}

Quantitative analysis of the elements in powder samples by LA-ICP-MS with PMMA powder as the binder and Cs as the internal standard

necessary for the realization of the definition of the new kilogram.

Removal of isobaric interferences in isotope dilution analysis of vanadium in silicon nitride fine ceramics powder by DRC-ICP-MS

A monitoring test for arsenic species in white rice flour was developed and applied to flours made from 20 samples of polished rice collected from locations all over Japan. The arsenic species in white rice flour made from five samples each of four types of rice were analyzed by HPLC-ICP-MS after a heat-assisted aqueous extraction. The total arsenic and major and minor element concentrations in the white rice flours were measured by ICP-MS and ICP-OES after microwave-assisted digestion. 91 ± 1% of the arsenic in the flours was extractable. Concentrations of arsenite [As(III)], arsenate [As(V)], and dimethylarsinic acid (DMAA) were closely positively correlated with the total arsenic concentrations. The total arsenic concentration in flours made from rice collected around Japan was 0.15 ± 0.07 mg kg(-1) (highest, 0.32 mg kg(-1)), which is very low. It was thus confirmed that the white rice flour samples collected in this experiment were not suffered from noticeable As contamination.

Accurate determination of arsenic in arsenobetaine standard solutions of BCR-626 and NMIJ CRM 7901-a by neutron activation analysis coupled with internal standard method.

The extraction of arsenic (As) species present in rice flour samples was investigated using different extracting solvents, and the concentration of each species was determined by HPLC-ICP-MS after heat-assisted extraction. The extraction efficiencies for total arsenic species and especially for arsenite [As(III)] and arsenate [As(V)] were investigated. As(III), As(V) and dimethylarsinic acid (DMAA) were found in the samples, and the concentration of DMAA did not vary with treatment conditions. However, the concentrations of extracted total arsenic and those of As(III) and As(V) depended on the extracting solvents. When an extracting solvent was highly acidic, the concentrations of extracted total arsenic were in good agreement with the total arsenic concentration determined by ICP-MS after microwave-assisted digestion, though a part of the As(V) was reduced to As(III) during the highly acidic extraction process. Extraction under neutral conditions increased the extracted As(V), but extracted total arsenic was decreased because a part of the As(III) could not be extracted. Optimum conditions for the extraction of As(III) and As(V) from rice flour samples are discussed to allow the accurate determinations of As(III), As(V) and DMAA in the rice flour samples. Heat block extraction techniques using 0.05 mol L(-1) HClO4 and silver-containing 0.15 mol L(-1) HNO3 were also developed.

Accuracy of the measurement of purity of sulfamic acid by coulometric titration

To realise highly efficient single-cell analysis of microbial cells by time-resolved inductively coupled plasma mass spectrometry (ICP-MS), we developed a modified high efficiency cell introduction system (HECIS), consisting of a large-bore high performance concentric nebulizer (LB-HPCN) with a centre capillary tube of 150 μm inner diameter and a custom-made small-volume (15 cm3) on-axis spray chamber that uses a sheath gas flow near the chamber exit to suppress cell deposition. We also assembled an external ion pulse counting unit to directly read the ion pulse current from the electron multiplier of the ICP-MS via a function generator with no dead time, in order to obtain data with sufficiently high time resolution (i.e., 0.05–1 ms). As compared to a conventional ICP-MS working at its minimum integration time (10 ms), this assembly led to more than ca. 13-fold higher signal-to-background ratios for 31P, and made higher throughput of cells to the plasma more feasible. By using the modified HECIS and the external ion pulse counting unit for determination of the cell introduction efficiencies of different-sized unicellular microbes, including yeast (Saccharomyces cerevisiae), cyanobacterium (Synechocystis sp. PCC 6803), red algae (Cyanidioschyzon merolae 10D and Galdieria sulphuraria), and green alga (Chlamydomonas reinhardtii CC-125), it was revealed that their cell introduction efficiencies ranged from 86% (for C. reinhardtii CC-125 with a mean cell diameter of 6.4 μm) to ca. 100% (for other microbes with mean cell diameters of 2.0–3.0 μm), implying that by use of the ICP-MS system, the cell introduction efficiencies are able to reach approximately 100% and tend to decrease with increasing cell sizes (at least more than 3.1 μm in mean diameter). A wide range of biologically important elements, such as C, Mg, Al, P, S, K, Ca, Cr, Mn, Fe, and Zn, were tested for reasonable detection using the ICP-MS system. Results likely corresponding to separate cell events were obtained for some elements present in each microbe.