Browsing by Author "Hoashi, Maki"

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    Development of methods for the determination of bismuth and thallium in geological materials and their significance for the Cretaceous-Tertiary boundary event : a thesis presented in partial fulfilment for the degree of Master of Science, Department of Chemistry and Biochemistry, Massey University, New Zealand
    (Massey University, 1988) Hoashi, Maki
    Solvent extraction methods have been developed for the determination of thallium and bismuth in rocks. The method for thallium is based on the extraction of the chlorocomplex into methylisobutyl ketone followed by removal of the interfering chloride ion as insoluble silver chloride. The method for bismuth is based on the extraction of a stable metal complex with ammonium pyrrolidine dithiocarbamate into methylisobutyl ketone. Both elements are analysed on a electrothermal graphite furnace atomic absorption spectrometer. Tests on the efficiencies of the methods showed a good precision and accuracy with limits of detection of 9.5 ng/ml (ppb) for thallium and 20 ng/ml (ppb) for bismuth. Recovery studies on synthetic samples showed recoveries of >99.9% for both elements. A geochemical study was performed on a Cretaceous-Tertiary boundary site located near Flaxbourne River, Ward, New Zealand. Investigations were carried out to determine the enrichment of thallium and bismuth in the stratigraphic column. The results show a good correlation between the iridium and thallium content throughout the rock sequence, but the samples have very low bismuth contents. This is indicative of the different geochemical behavior of bismuth to other chalcophiles. These findings do not contradict the impact theory initially hypothesized by Alvarez et al. (1980), and instead suggest that bismuth's mobility and solubility are far greater than those of thallium and the other chalcophile elements enriched in the Flaxbourne River sequence. This results in the leaching of bismuth from the stratigraphic column by sea water after deposition.
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    The platinum group metals in iron meteorites : thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Chemistry, Department of Chemistry and Biochemistry, Massey University, Palmerston North, New Zealand
    (Massey University, 1990) Hoashi, Maki
    Solvent extraction methods have been developed for the determination of Ru, Pd and Pt in iron meteorites. The method for Ru is based on the oxidation of this element in HCl solutions with sodium periodate followed by extraction of the tetroxide into CHCl3. The CHCl3 phase is then removed to a HNO3-NaIO4 "keeper" solution for storage up to 17 hours prior to analysis. The method for Pd and Pt entails simultaneous extraction of their stable iodocomplexes into methylisobutyl ketone after removal of Fe(III) as the chlorocomplex. The digestion of the samples with reference to these elements has also been investigated. All three elements were determined by the graphite furnace atomic absorption spectrometry technique. The limit of detection was lowered by increasing the volume of organic phase placed in the graphite furnace. The lowest absolute detection limits achieved in this study were 0.5 ng for Ru, 0.5 ng for Pd and 5 ng for Pt. The platinum group metal values for 108 authentic iron meteorites were subjected to Principal Components Analysis and Discriminant Analysis. These procedures confirmed the validity of the classification of iron meteorites developed over the past 25 years, but highlighted poor fits for some individual iron meteorites within a group. Possible reclassification of these members was evaluated after consideration of the meteorite's morphological features. The cases for the merging of some groups were investigated and discussed with reference to the chemical features of those groups. The data obtained also revealed several cases of meteorite pairings (related members of a single meteorite shower catalogued as separate meteorites), instances of the mislabelling of museum fragments and two putative meteorites which proved to consist of man-made materials.