Takayoshi Kuroiwa

The extraction and speciation of arsenic in rice flour by HPLC–ICP-MS

Several solvent mixtures and techniques for the extraction of arsenic (As) species from rice flour samples prior to their analysis by HPLC-ICP-MS were investigated. Microwave-assisted extraction using water at 80 degrees C for 30 min provided the highest extraction efficiency. Total recoveries of extracted As species were in good agreement with the total As concentrations determined by ICP-MS after microwave-assisted acid digestion of the samples. Arsenite [As(III)], arsenate [As(V)] and dimethylarsinic acid (DMAA) were the main species detected in rice flour samples.

Study on simultaneous speciation of arsenic and antimony by HPLC-ICP-MS

A method was developed for the simultaneous speciation of arsenic and antimony with HPLC-ICP-MS using C30 reversed phase column. Eight kinds of arsenic compounds (As(III), As(V), monomethylarsonic acid (MMAA), dimethylarsinic acid (DMAA), arsenobetaine (AB), arsenocholine (AsC), trimethylarsine oxide (TMAO) and tetramethylarsonium (TeMA)), Sb(III) and Sb(V) were simultaneously separated by the special mobile phase containing ammonium tartrate. Especially for the species of organic As, a C30 column was better than a C18 column in the effect of separation. Limits of detection (LOD) for these elements were 0.2 ng ml(-1) for the species of each As, and 0.5 ng ml(-1) for the species of each Sb, when a 10 microl of sample was injected, respectively. The proposed method was applied to a hot spring water and a fish sample.

Rapid determination of arsenic species in freshwater organisms from the arsenic-rich Hayakawa River in Japan using HPLC-ICP-MS

Speciation analyses of water-soluble arsenicals from freshwater and biological samples collected from the Hayakawa River (Kanagawa, Japan), which contains a high concentration of arsenic, were performed using high performance liquid chromatography/inductively coupled plasma mass spectrometry (HPLC-ICP-MS). River water contained only arsenate, which is a pentavalent inorganic arsenical. The water bug Stenopsyche marmorata contained inorganic arsenicals accounting for 77% of the water-soluble arsenicals, followed by oxo-arsenosugar-glycerol, which is a type of dimethylarsinoylriboside (arsenosugar). The freshwater green macroalga Cladophora glomerata contained oxo-arsenosugar-glycerol and oxo-arsenosugar-phosphate as 64% of the water-soluble arsenicals. Production of the same types of arsenosugars was confirmed in the freshwater green microalga Chlamydomonas reinhardtii CC125 experimentally exposed to arsenate. The muscle tissues of all freshwater fish and crustaceans analyzed contained arsenobetaine, oxo-arsenosugar-glycerol, and/or oxo-arsenosugar-phosphate in various concentrations. Seven freshwater fish (Cobitis biwae, Leuciscus hakonensis, Phoxinus lagowski steindachneri, Plecoglossus altivelis, Rhinogobius sp. CB, Rhinogobius sp. CO, Sicyopterus japonicus) and the crustacean Macrobracbium nipponenese contained arsenobetaine in their muscle tissues as the predominant form, contributing up to 80% of the water-soluble arsenicals, while the freshwater fish Anguilla japonica muscle tissues primarily contained dimethylarsinic acid as 77% of the water-soluble arsenicals, followed by arsenobetaine. The freshwater fish Zacco platypus muscle tissues predominantly contained oxo-arsenosugar-phosphate, accounting for 51% of the water-soluble arsenicals, followed by dimethylarsinic acid and arsenobetaine. These biological samples possessed non-extractable arsenical(s) accounting for more than 50% of the total arsenic concentration.

Arsenic compounds in the freshwater green microalga Chlorella vulgaris after exposure to arsenite

The freshwater green alga, Chlorella vulgaris, was cultivated in a modified Detmer medium in the presence of arsenite in order to investigate tolerance, accumulation, transformation and excretion of arsenic species. When the alga was exposed to arsenite, arsenic accumulation markedly increased in the beginning of the log phase, rose to a maximum of 610 μg As g -1 and then decreased during the period from 40 to 120h after inoculation. Arsenate was the major metabolite in the algal cell; trimethylarsenical species (TMA) were also found 36 h after inoculation when the alga was exposed to arsenite at levels of 70 - 100 μg As cm -3 . At arsenite levels of 10-20 μg As cm -3 , cell growth was higher than in an arsenic-free medium. Arsenite accumulated in Chlorella vulgaris was transformed to arsenate through bio-oxidation and to a small degree to methyl-, dimethyl-, and trimethyl-arsenic species through biomethylation. Furthermore, the arsenic metabolites were readily excreted under conditions undesirable for the growth of the alga. Total arsenic accumulation decreased with an increase in arsenite concentration in the medium.

Mechanism of sensitivity difference between trivalent inorganic As species [As(III)] and pentavalent species [As(V)] with inductively coupled plasma spectrometry.

The pentavalent inorganic arsenic (As) species [As(V)] is found to be 4% more sensitive than the trivalent species [As(III)] with inductively coupled plasma mass spectrometry (ICP-MS) and inductively coupled plasma optical emission spectrometry (ICP-OES). Although there was no sensitivity difference between As(III) and As(V) with atomic absorption spectrometry (AAS), electrothermal atomization atomic absorption spectrometry (ETAAS), X-ray fluorescence (XRF), and neutron activation analysis (NAA). The calibration solutions of As(III) and As(V) were gravimetrically prepared from the unique mother standard solution of JCSS As standard solution which is certified by Japan Calibration Service System (JCSS). Since it is essential to use the calibration solutions with exactly the same concentration of As in order to accurately compare the sensitivities between As(III) and As(V). The mechanisms of this sensitivity difference between them were investigated by ICP-MS and ICP-OES, and it elucidated that the formation rates of hydride polyatomic species of As were definitively different between As(III) and As(V) species in the plasma. This phenomenon directly affected their sensitivities with ICP-MS and ICP-OES.

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

Following online publication the authors regrettably found some mistakes and typographical errors in the article. The corrections are given below. Page 1714, section “Apparatus”, the end of the first paragraph should read: “And, He 1 mL/min + H2 3 mL/min was used for the measurement of Fe and He 3 mL/min + H2 1 mL/min was used for other elements”. Page 1714, section “Apparatus”, the third paragraph should read: “The typical operating parameters for the ICP-OES were as follows” Page 1716, section “Homogeneity study”, the end of the first paragraph should read: “The sbb was theoretically calculated from Mswithin and Msamong.” Page 1716, section “Homogeneity study”, equation 1 should read:

Proficiency testing for determination of pesticide residues in soybean: comparison of assigned values from participants' results and isotope-dilution mass spectrometric determination.

Proficiency testing (PT) for the determination of pesticide residues in soybean samples was organized by the National Metrology Institute of Japan (NMIJ). The candidate certified reference material, NMIJ CRM 7509-a, that was prepared from the raw soybeans containing target pesticides (diazinon, fenitrothion, chlorpyrifos, and permethrin) was used as the test sample. Forty participants submitted two sets of analytical results along with the details of the analytical method and conditions they applied. Two types of assigned values were established for each target pesticide: one was derived from the analytical results of the participants, and the other was provided from the analytical results by isotope-dilution mass spectrometry (IDMS). The latter values were 7.4-16% higher than the former values, plausibly because the analytical values from the IDMS measurements were not affected by the recovery ratio of the target pesticides during the analytical process. Thus, two kinds of z-scores were calculated for individual participants using the corresponding assigned values: one (z1-score) showed the relative performance score for the present PT and the other (z2-score) could be used for evaluation of the trueness of their analytical methods.

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.

Neutron activation analysis (NAA) coupled with an internal standard method was applied for the determination of As in the certified reference material (CRM) of arsenobetaine (AB) standard solutions to verify their certified values. Gold was used as an internal standard to compensate for the difference of the neutron exposure in an irradiation capsule and to improve the sample-to-sample repeatability. Application of the internal standard method significantly improved linearity of the calibration curve up to 1 microg of As, too. The analytical reliability of the proposed method was evaluated by k(0)-standardization NAA. The analytical results of As in AB standard solutions of BCR-626 and NMIJ CRM 7901-a were (499+/-55)mgkg(-1) (k=2) and (10.16+/-0.15)mgkg(-1) (k=2), respectively. These values were found to be 15-20% higher than the certified values. The between-bottle variation of BCR-626 was much larger than the expanded uncertainty of the certified value, although that of NMIJ CRM 7901-a was almost negligible.

Differences in sensitivity between As(III) and As(V) measured by inductively coupled plasma spectrometry and the factors affecting the incoherent molecular formation (IMF) effect in the plasma

When inorganic As species [As(III) and As(V)] and Se species [Se(IV) and Se(VI)] are measured by inductively coupled plasma spectrometry, As(V) is found to be more sensitive than As(III), although Se(IV) and Se(VI) show the same sensitivity. The mechanism of the sensitivity difference between As(V) and As(III) was investigated using ICP-sector field mass spectrometry (ICP-SFMS), and it was elucidated that the amount of hydride polyatomic species of As formed in the plasma was different between As(V) and As(III). The formation of polyatomic species depends upon the oxidation state of the As atoms in the plasma, we describe this phenomenon as the incoherent molecular formation (IMF) effect. The mechanisms of the IMF effect were further investigated and techniques for removing its influence on As determination are discussed.

Selective encapsulation of cesium ions using the cyclic peptide moiety of surfactin: Highly efficient removal based on an aqueous giant micellar system

Cyclic peptide of surfactin (SF) is one of the promising environment-friendly biosurfactants abundantly produced by microorganisms such as Bacillus subtilis. SF is also known to act as an ionophore, wherein alkali metal ions can be trapped in the cyclic peptide. Especially, SF is expected to show high affinity for Cs(+) because of the distinctive cavity size and coordination number. In this study, we reported the specific interaction between SF and Cs(+) and succeeded in the highly efficient removal of Cs(+) from water using giant SF micelles as a natural sorbent. The specific interaction between SF and Cs(+) to form their inclusion complex was revealed by nuclear magnetic resonance (NMR) and Fourier transform infrared (FT-IR) spectroscopy. We found that SF micelles selectively encapsulate Cs(+), which was suggested by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS). A highly effective separation of Cs(+) immobilized on the surface of the SF micelles was also achieved through facile centrifugal ultrafiltration in 91% even in coexisting with other alkali metal ions such as Na(+) and K(+). Thus, the use of the giant micellar system of SF with its high Cs(+) affinity and distinctive assembling properties would be a new approach for the treatment of contaminated soil and water.