Kenji Isshiki

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.

Determination of Arsenite, Arsenate, and Monomethylarsonic Acid in Seawater by Ion-exclusion Chromatography Combined with Inductively Coupled Plasma Mass Spectrometry Using Reaction Cell and Hydride Generation Techniques

This paper describes a robust and sensitive method for the determination of arsenic species in seawater by ion-exclusion liquid chromatography (LC) combined with inductively coupled plasma mass spectrometry (ICP-MS) using reaction cell and hydride generation (HG) techniques. A good separation of arsenite, arsenate, and monomethylarsonic acid was achieved using an ion-exclusion column packed with a sulfonated polystyrene resin and a dilute nitric acid at pH 2.0 as the eluent, even when a large volume, i.e. 200 mul, of seawater samples containing a large amount of matrix was repeatedly injected. Separations of the chloride ion due to the matrix and arsenic species were partially performed; however, the extensive peak of ArCl due to high content of Cl(-) in a sample overlapped peaks of the three arsenic species on (75)As measurement by ICP-MS. This ArCl polyatomic interference was efficiently eliminated by collision of ArCl molecules with helium in an octopole reaction cell which was introduced prior to a mass spectrometer. Detection limits of the three arsenic species in a sample containing 2% Cl(-), the concentration of which is comparable to that in a seawater sample, by LC-ICP-MS with the octopole reaction system (ORS), ranged from 21 to 25 pg As ml(-1); these values were three-six times lower than those by LC-ICP-MS without ORS. As another technique for ArCl interference elimination, HG prior to ICP-MS was also successfully used not only to reduce the interference but also to improve the detection limits to 3.4-4.5 pg As ml(-1). The developed LC-ICP-ORS-MS and LC-HG-ICP-MS were validated by analyzing a certified reference material (CRM) of seawater. In addition, no serious decrease in analytical performance of present methods was observed in the experimental periods of half a year for LC-ICP-ORS-MS and 1 year for LC-HG-ICP-MS, respectively. The latter method was successfully applied to characterize seasonal variations of three arsenic species in deep seawater and surface seawater.

Hydrothermal plumes at the Rodriguez triple junction, Indian ridge

Water column anomalies of light transmission, Mn, Fe, Al and CH4 concentrations were searched in the central, southeastern and southwestern Indian Ridge segments centered on the Rodriguez Triple Junction (RTJ) (∼25°32′S, ∼70°02′E), for the purpose of locating hydrothermally active areas, in July to August 1993. We found an active zone in the central Indian Ridge segment (25°18–20′S) approximately 12 miles north of the RTJ, where significant hydrothermal plumes were observed at 2,200–2,400 m depth. Intensive tow-yo observations using a CTD rosette multi-sampling system equipped with a transmissometer revealed that the plumes show temporal as well as spatial variations. Discrete water samples within the plumes were enriched in Mn, Fe, and CH4, with maximum concentrations of 9.8 nM, 40.2 nM and 3.3 nM, respectively. Judging from the spatial and chemical characteristics of the plumes, especially from transmission anomalies andC/H4Mn ratios, we speculate that the hydrothermal venting site might be not in the rift valley but on the eastern off-axis zone, several miles distant from the rift valley.

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.

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.

Determination of germanium by graphite-furnace atomic-absorption spectrometry

The premature loss of germanium as volatile GeO results in low sensitivity and poor reproducibility in the determination of germanium by graphite-furnace atomic-absorption spectrometry. This interference can be eliminated by suppressing the premature reduction of GeO(2) to GeO during the ashing step, and dissociating the germanium oxides into the atoms simultaneously with their vaporization during the atomization step. The premature reduction of GeO(2) to GeO has been successfully prevented by several approaches: (1) diminishing the reducing activity of the graphite furnace by (a) oxidizing the graphite surface and intercalating oxygen into the graphite lattice with oxidizing acids, such as nitric or perchloric, in the sample solution, or (b) using a tantalum-treated graphite furnace; (2) keeping the analyte as germanium (IV) by addition of sodium or potassium hydroxide to the sample solutions.

Form of dissolved silicon in seawater

Abstract Concentrations of dissolved silicon in 83 seawater samples obtained from various depths at seven stations in the North Pacific, the Japan Sea, and the Eastern China Sea were determined by the molybdenum blue method and by inductively coupled argon plasma atomic emission spectrometry. The silicon concentrations ranged from 0.6 to 169.0 μmol l −1 at the North Pacific stations, from 1.9 to 83.3 μmol l −1 at the Japan Sea stations, and from −1 at the Eastern China Sea stations. The concentrations obtained by the two methods were the same within experimental error, indicating that dissolved silicon is present in seawater as ‘reactive silica’. Other silicon species cannot be present at concentrations higher than a few micromoles per liter.

Determination of ultratrace amounts of cobalt by catalysis of the tiron-hydrogen peroxide reaction with an improved continuous-flow analysis system.

An improved continuous-flow analysis method has been designed and applied to the determination of ultratrace amounts of cobalt(II) by the catalysis of the tiron-hydrogen peroxide reaction in basic medium. From 3 to 5000 pg of cobalt(II) in 1 ml of acidified sample can be determined at a sampling rate of 40 samples/hour. The relative standard deviations (10 replicates) are 1% at the 100 pg/ml level and 3% at 10 pg/ml.

Studies of a sample injection method for introducing metal β-diketonates into an inductively-coupled plasma

Abstract As a method for sample injection into an ICP, batch injection of volatile metal chelates was investigated. The sample solution of metal chelates dissolved in organic solvent was injected with a microsyringe into the carrier gas containing the ligand vapour in order to prevent the decomposition of the chelates. With this method, calibration curves of five metals such as Al, Be, Cr, Cu and Fe, whose linear range is over three orders of magnitude, were obtained after optimization of operating conditions. Sub-nanogram amounts of metal chelates in microliter samples could be determined with a relative standard deviation of a few percent.