Yoshiki Sohrin

Multielemental Determination of GEOTRACES Key Trace Metals in Seawater by ICPMS after Preconcentration Using an Ethylenediaminetriacetic Acid Chelating Resin

GEOTRACES is an international research project on marine biogeochemical cycles of trace elements and their isotopes. GEOTRACES key trace metals in seawater are Al (8-1000 ng/kg), Mn (4-300 ng/kg), Fe (1-100 ng/kg), Cu (30-300 ng/kg), Zn (3-600 ng/kg), and Cd (0.1-100 ng/kg), of which global oceanic distribution will be determined on a number of research cruises. This work introduces a novel method of solid-phase extraction to determine Al, Mn, Fe, Co, Ni, Cu, Zn, Cd, and Pb in seawater by adjusting the pH of the sample to 6 and carrying out a single preconcentration step. The trace metals were collected from approximately 120 mL of seawater using a column of a chelating resin containing the ethylenediaminetriacetic acid functional group and eluted with approximately 15 mL of 1 M HNO3. Mn and Fe in the eluate were measured by inductively coupled plasma mass spectrometry (ICPMS) using the dynamic reaction cell mode, and the other metals were measured using the standard mode. Using this procedure, the trace metals were collected quantitatively, while >99.9% of alkali and alkaline earth metals in seawater were removed. The procedural blank was <7% of the mean concentration in deep ocean waters, except 16% for Pb. The overall detection limit was <14% of the mean concentration in deep ocean waters. The RSD was <9%. Our values for the trace metals in the certified reference materials of seawater NASS-5 and nearshore seawater CASS-4 agreed with the certified values (except that there is no certified value for Al). This method was also successfully applied to the reference materials of open-ocean seawater produced by the SAFe program. Our Fe concentrations were 5.9 +/- 0.7 ng/kg for surface water (S1) and 50.4 +/- 2.9 ng/kg for deep water (D2), which are in agreement with the interlaboratory averages of 5.4 +/- 2.4 and 50.8 +/- 9.5 ng/L, respectively. The data for other metals were oceanographically consistent.

Biosynthesis and release of methylarsenic compounds during the growth of freshwater algae.

Arsenic transformations by freshwater algae have been studied under laboratory conditions. By the use of a new analytical method, we identified methylarsenic(III) species in the growth medium of green-alga Closterium aciculare incubated under axenic conditions. The arsenate concentration in the experimental medium began to decrease just after inoculation, and the levels of arsenite and methylarsenicals increased with the growth of C. aciculare. Initially, most of the arsenate was converted into arsenite, which peaked in concentration during the exponential phase. Methylarsenicals accumulated rapidly in the stationary phase. DMAA(V) production was enhanced when the ratio of phosphate to arsenate decreased in the culture medium. The levels of DMAA(V) increased continuously toward the end of the experiment. On the other hand, methylarsenic(III) species remained relatively steady during the stationary phase. Methylarsenic(III) species accounted for 0-35% of methylarsenicals. These results suggest that arsenite and methylarsenicals (containing methylarsenic(III) species) are supplied by phytoplankton, and serve as evidence of the origin of methylarsenic(III) species in natural waters.

Preconcentration of chromium(III) and chromium(VI) in sea water by complexation with quinolin-8-ol and adsorption on macroporous resin

Abstract Chromium(III) is a sea water at the nanomole level was selectively collected using a column packed with macroporous polystyrene-divinylbenzene resin after complexation with quinolin-8-ol. Complex formation between ligand and inert hydrated chromium(III) ions was achieved by heating a sample solution containing a small amount of quinolin-8-ol for a short time in a microwave oven. Chromium(VI) was collected by a similar method after reducing it to chromium(III) with hydroxylamine. The effect of co-existing organic materials on the collection of chromium(III) and chromium(VI) was examined. This method was successfully applied to the determination of chromium(III) and chromium(VI) in sea water by graphite furnace AAS.

Determination and distribution of iodide- and total-iodine in the North Pacific Ocean - by using a new automated electrochemical method

Abstract A new automated analytical method for determining inorganic iodine species in seawater as iodide- and total-iodine (iodide+iodate), by using a flow-through electrode system, has been applied to the seawater samples collected from the adjacent seas of Japan and the western and central North Pacific Ocean. It was found that a considerable amount of iodide-iodine is distributed not only in the euphotic zone, but also in deep waters of the Japan Sea and the Japan Deep and in directly overlying waters on the sea floor of the open ocean. This fact suggests that the reduction of iodate to iodide by biological activity in seawater occurs when nitrate is consumed by nitrate respiration in the presence of a large amount of easily oxidizable organic matter, which may be in particulate form, rather than when nitrate is deficient, as is generally accepted, because these waters contain the usual amount of nitrate for deep waters.

Distribution of trace bioelements in the subarctic North Pacific Ocean and the Bering Sea (the R/V Hakuho Maru Cruise KH-97-2)

A column concentration-high resolution inductively coupled plasma mass spectrometry (ICP-MS) determination was applied to measure the total dissolved concentrations of Fe, Co, Ni, Cu and Zn in seawater collected from the subarctic North Pacific (~45°N) and the Bering Sea in July–September 1997. Total adsorbable Mn was determined on board by column electrolysis preconcentration and chemiluminescence detection. The vertical profiles for Fe, Ni and Zn were nutrient-like. The deep water concentration of Fe was ~0.5 nM in the northeast Pacific (18°-140°W) and increased to ~1 nM in the northwest Pacific (161°E) and ~2 nM in the Bering Sea (57°N, 180°E). The deep water concentrations for Ni and Zn in the Bering Sea were also 1.3–2 times higher than in the North Pacific. The profiles for Co and Cu were examined in the subarctic North Pacific, and results obtained were consistent with previous reports. There was a significant correlation between the concentrations of Co and Mn except for surface mixed layer. The profiles for total adsorbable Mn were similar to the reported profiles for total dissolvable Mn. The deep water concentration of Mn in the Bering Sea was also 4 times higher than in the North Pacific. Iron and zinc were depleted in surface water of the subarctic North Pacific. The relationship between these trace elements and nutrients suggests that these elements could be a limiting factor of phytoplankton productivity. In the Bering Sea, surface water contained ~0.3 nM of Fe. The Zn concentration, which was less than the detection limit in surface water, increased at shallower depths (~30 m) compared with the subarctic North Pacific. These results imply a higher flux of Fe and Zn to surface water in the Bering Sea. This in turn may cause the ecosystem in the Bering Sea characterized by a dominance of diatoms and high regenerated production.

Tungsten in North pacific waters

Tungsten in oceanic waters has only been analysed in a few coastal areas. Here, we report the first tungsten depth profiles in oceanic waters. Tungsten concentration in the north Pacific is constant at 53–60 pmol l−1 (normalized to a salinity of 35‰) from the surface to the bottom. Similar vertical profiles of tungsten and molybdenum probably result from the fact that both elements are hardly adsorbed at all onto organisms and particulate organic matter in surface waters. However, although the crustal abundance of tungsten and molybdenum are nearly equal, the concentration of tungsten is ∼ 11800 of that of molybdenum in oceanic waters. This indicates that tungsten is removed from seawater much more rapidly than molybdenum, by adsorption onto ferric hydroxide, manganese oxide and clay minerals.

Arsenic speciation including 'hidden' arsenic in natural waters

Recent studies indicate the existence in natural waters of ‘hidden’ arsenic which had previously been undetected by the hydride generation technique. A speciation method for arsenic species has been developed in which hidden arsenic was classified into two fractions by their lability to the photochemical degradation procedure: the ultraviolet-labile fraction and the ultravioletresistant fraction. The ultraviolet-labile fraction was the major fraction of hidden arsenic and comprised 15‐45% and 4‐26% of the total arsenic in Uranouchi Inlet and Lake Biwa (Japan), respectively. The highest concentration of the ultraviolet-resistant fraction was observed in Uranouchi Inlet during the summer, in which dimethylarsinic acid increased in the water column. We discuss the hidden arsenic fraction as the key to explaining arsenic speciation in natural waters. Copyright # 1999 John Wiley & Sons, Ltd.

Iron-catalyzed aromatic amination for nonsymmetrical triarylamine synthesis.

Novel iron-catalyzed amination reactions of various aryl bromides have been developed for the synthesis of diaryl- and triarylamines. The key to the success of this protocol is the use of in situ generated magnesium amides in the presence of a lithium halide, which dramatically increases the product yield. The present method is simple and free of precious and expensive metals and ligands, thus providing a facile route to triarylamines, a recurrent core unit in organic electronic materials as well as pharmaceuticals.

Dissolved niobium and tantalum in the North Pacific

Niobium and tantalum were measured in North Pacific seawater. The concentration of Nb shows a slight depletion in surface water and that of Ta shows a slight increase near the bottom. The mean concentrations of Nb in surface and deep Pacific water are 3.0 and 3.8 pmol/kg, respectively, and for Ta, 0.08 and 0.20 pmol/kg. Their relatively uniform distribution suggests that Nb and Ta are less reactive with particles in seawater than Zr and Hf. In analogy with V, the species of Nb and Ta may be oxyacids rather than hydroxides.

Simultaneous determination of tungsten and molybdenum in sea water by catalytic current polarography after preconcentration on a resin column

Abstract The simultaneous determination of tungsten and molybdenum in sea water is based on preconcentration by column extraction with 7-(1-vinyl-3,3,5,5-tetramethylhexyl)-8-quinolinol (Kelex- 100) resin, and measurement of the polarographic catalytic currents obtained in a solution of chlorate, benzilic acid and 2-methyl-8-quinolinol. When the concentration factor is 50, the detection limits are 2.4 pM for tungsten and 17 pM for molybdenum (for a signal-to-noise ratio of 3). The precision of the determination is ca. 10% for 67 pM tungsten and ca. 5% for 106 nM molybdenum in sea water ( n =4). Results for sea water and other natural waters are presented.