Shizuko Hirata

Trace metal enrichment by automated on-line column preconcentration for flow-injection atomic absorption spectrometry

An on-line column preconcentration technique for flow-injection atomic absorption spectrometry was developed. Diverse metal ions (Cd2+, Zn2+, Cu2+, Mn2+, Pb2+, Fe3+ and Cr3+) in solution were concentrated quantitatively by a microcolumn (7-mm × 4-mm i.d.) packed with Muromac A-1, which is an iminodiacetate chelate resin, in a flow-injection system. From the pH dependence of the uptake of the ions, all the divalent metals examined were recovered quantitatively in the pH range 3–5 and the trivalent metals were recovered at a maximum pH of 1. Enrichment factors using 20-ml samples were in the range 90–180-fold for the seven elements and the sampling rate was 13 h−1. The 3σ detection limits were in the range 0.14–2.1 μg l−1 and the relative standard deviations for replicate measurements (n=3–4) were in the range 0.7–1.7%. The method was compared with flame and graphite furnace atomic absorption spectrometry. Application to the determination of cadmium and copper in several standard reference materials is described.

Determination of chromium(III) and total chromium in seawater by on-line column preconcentration inductively coupled plasma mass spectrometry☆

Abstract An automated low-pressure flow injection method with on-line column preconcentration using inductively coupled plasma mass spectrometry is described for the determination of chromium(III) and total chromium in seawater. A home-made column of commercially available iminodiacetate resin, Muromac A-1, was used to concentrate chromium(III) in seawater at a pH of 3.0. Following washing of the column with water, the chromium(III) was eluted and transferred to the plasma with 0.70 M nitric acid. Total chromium was determined after the reduction of chromium(VI) to chromium(III) with a 2-mM hydroxylamine solution at pH 1.8. Detection limit (three times the relative standard deviation of the background) of chromium(III) in the artificial seawater based on eight replicate measurements was 0.020 ng ml −1 with a sample loading time of 120 s. The precision was ±1.9%. One sample can be processed in 5 min. Calibration was accomplished by means of artificial seawater. The proposed method was verified by the analysis of two Reference Standard Materials of seawater NASS-4 and CASS-3.

Stability constants for the complexes of transition-metal ions with fulvic and humic acids in sediments measured by gel filtration.

The molecular-weight distributions of fulvic and humic acids in sediments and their complexes with metal ions (Cu(2+), Zn(2+), Mn(2+)) were investigated by gel filtration. In all cases, metal complexes were found in the fulvic and humic acids. In the complexes the metals were bound to the high molecular-weight fulvic and humic polymers. By use of gel filtration, stability constants for the complexes of copper, zinc and manganese with fulvic acids have been measured. Scatchard plots indicate the presence of two classes of binding site with stability constants of 2.3 x 10(7) and 1.4 x 10(6) for copper, 2.1 x 10(6) and 6.6 x 10(4) for zinc and 1.8 x 10(5) and 7.3 x 10(3) for manganese, respectively.

Phosphorus and metals bound to organic matter in coastal sediments - An investigation of complexes of P, Cu, Zn, Fe, Mn, Ni, Co and Ti by inductively coupled plasma-atomic emission spectrometry with sephadex gel chromatography

Abstract Phosphorus and metals bound to organic matter were separated from coastal sediments of Harima Sound in Seto Inland Sea, Japan by extraction with NaOH and fractionated by Sephadex G-25 chromatography. Phosphorus and metals were determined in the eluates by a multi-channel, inductively coupled plasma-atomic emission spectrometer. Phosphorus and Cu, Zn, Fe, Mn, Ni, Cr, Co and Ti bound to organic matter with high molecular weights (OMHMW) (MW ⩾ 5000) were found to be present in the sediments, but no Mo or V were found. The technique provides minimum estimates of the amounts of P and metals bound to organic matter. These organic complexes show surface enrichment in a sediment core (0–20 cm) and their contents decrease with depth. Also, the amounts of eighteen elements, namely: P, Fe, Mn, Zn, Cu, Si, Al, Ti, Pb, Co, Ni, Cr, Mo, V, Na, K, Ca and Mg, in H 2 O, ammonium acetate at pH 7 and 5, hydrogen peroxide, hydroxylamine hydrochloride and hydrogen fluoric acid soluble fractions have been determined with a selective chemical leaching technique for the 210 Pb-dated sediment core sample. Considerable amounts of P (6–19%) and Cu (5–21%) were associated with organic matter, in contrast to other metals such as Fe, Mn, Zn, Ni, Cr, Co and Ti which were associated with sulfide and silicate.

Trace metals in humic substances of coastal sediments of the Seto Inland Sea, Japan

Abstract The contents of major elements and trace metals have been determined in sediments and associated humic acids from the Seto Inland Sea, Japan. The principal trace element components of the humic acids that passed through a cation-exchange column were phosphorus (1700–2700 μg g −1 ) and copper (700–1300 μg g −1 ). Elements enriched in the humic acids compared with the sediments included P, Cu, Fe, Al, Zn, Mo and Ni, whereas the concentrations of Ti, Mn, Ba, Co, Cr, B, V and Pb were much lower in the humic acids. Enrichment factors for P, Cu, Ni and Zn became larger as the overlying water depth became deeper. The coastal humic acids contained 0.16–0.30% P and 2.21–2.85% S, with C/P atomic ratios of 495–952 (average, 770) and C/S atomic ratios of 54.5–71.8 (average, 61.2). Diagenesis of sedimentary humic acids produces humic acids with C/P atomic ratios of 1000 by preferential loss of phosphorus, as well as of organic carbon and nitrogen.

Molecular weight and trace metal distributions in fulvic and humic acid fractions of coastal marine sediments

Molecular weight and trace metal distributions of fulvic and humic acid fractions of marine sediments from the Seto Inland Sea were investigated by using a gel filtration technique in combination with atomic absorption and emission spectrometries. A binary molecular weight distribution was found both in the fulvic acid fraction and in the humic acid fraction. The fulvic acid fractions with molecular weights of less than 1.5×103 and of 5×103−104 accounted for 38–57 % and 25–41 % of the total fulvic acids, respectively, and the humic acid fractions with molecular weights of 102−104 and of over 2×105 accounted for 58–73 % and 16–27 % of the total humic acids, respectively. The components with molecular weights of over 1.5×103 contained 54 %, on average, of the Fe, Zn and Cu in the fulvic acid fraction, and the components with molecular weights of over 104 contained 58 %, on average, of these metals in the humic acid fraction.

Speciation of Dissolved Metals Associated with Organic Matter in Coastal Seawaters

By combined use of chloroform extraction and Amberlite XAD-2 resin chromatography, metal-organic compounds dissolved in coastal seawaters of Harima Sound, the Seto Inland Sea, were separated into three groups: hydrophobic, hydrophilic neutral and basic, and hydrophilic acidic. The hydrophobic metal-organic compounds, which are associated with organic matter with molecular weight less than 300, accounted for only a small fraction of the metal-organic compounds; 6 % for Cu and an insignificant fraction for Fe, Mn and Zn. The hydrophilic metal-organic compounds with molecular weights between 100 and 1,500 were major components of the metal-organic compounds. The metals associated with the organic matter on average accounted for 12 % of the Fe, 11 % of the Mn, 7 % of the Zn and 23 % of the Cu of the reactive dissolved metals.

Behavior of manganese in aqua-benthic environment in the Hiro Bay

The horizontal and vertical distributions of manganese in sea water, interstitial water and sediments in the Hiro Bay, Seto Inland Sea, Japan, have been investigated. The outflow from a pulp mill is the primary source of manganese in this bay. The industrial waste water contained 0.19 mg l−1 of manganese, mostly in a dissolved form. This manganese diffused out both horizontally and vertically into the surrounding sea water. The content of manganese in the liquid and solid phases in the sediments, however, are inverse with that in the sea water; namely the lowest concentration of manganese in the sediments was observed at the station near the outfall and manganese concentration increased with the distance from the outfall.

The Occurrence of Organic Peroxides in Seawater

Organic peroxides (ROOH), as well as hydrogen peroxide (H2O2), dissolved in seawater were determined by fluorometry. Seawater samples were collected at Hiroshima Bay and the Iyo-Nada in the Seto Inland Sea, western Japan in May 1995. Using an enzymatic destruction method, ROOH and H2O2 were descriminated from each other. The concentration of ROOH measured was in the range of 38–389 nM in seawater samples, whereas the H2O2 concentration was in the range of 0–195 nM. The vertical distribution (0–45 m depth) of ROOH in seawater was found to be almost uniform or a little higher at the bottom layer waters, whereas the H2O2 concentration was highest at surface waters and decreased with depth. Linear regression analysis was conducted to examine the correlations between peroxide concentrations and other analytical items such as CTD data, nutrients, fluorescent organic matter and dissolved organic carbon. The results showed that the ROOH concentration has almost no correlation with other parameters, whereas the H2O2 concentration highly correlates with the salinity in the Hiroshima Bay samples but mostly correlates with water temperature in the Iyo-Nada samples. These results clearly indicate that the generation and decomposition mechanism of ROOH is different from that of H2O2.