Browsing by Author "Guo, Xun"

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    A hydride generation-atomic absorption spectrometric procedure for the quantification of germanium and other elements in iron meteorites : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science, Department of Chemistry and Biochemistry, Massey University, New Zealand
    (Massey University, 1989) Guo, Xun
    Covalent hydride-forming elements were investigated to explore their potential use in chemical classification of iron meteorites. Only As, Ge and Pb were detectable in these samples. A simple and inexpensive combined hydride generation atomic absorption spectrometric method (HGAAS) was developed and was the first to be applied to quantification of these elements in iron meteorites. Variable studies were: flame type, generation reaction conditions, interferences, and atomization. A convenient nitrogen-hydrogen-air entrained flame was used to determine germanium in meteorites. The determination of germanium in 22 iron meteorites using the above method gave data in good agreement with those obtained by J.T Wasson et al who used radiochemical neutron activation analysis (RNAA). From practical applications of my method, it was clear that the technique afforded a reliable, inexpensive, and sensitive method for me quantification of germanium in iron meteorites. Various methods of sample attack were tried and included acid attacK in an open container, under a reflux, or with a Teflon bomb, and fusion with sodium peroxide. The optimum method was acid attack under reflux or with a Teflon bomb. Nitric acid was more suitable than other acids. The method has applied to various samples which resulted in: identification of a bogus meteorite(HANAU), classification of a newly discovered meteorite(TASSAJARA), and confirmation that the Antarctic "ONNUM VALLEY" iron was in fact part of the previously known DERRICK PEAKS shower.
  • Thumbnail Image
    Item
    Quantification of gallium, indium and thallium in meteorites and other geological materials by graphite furnace atomic absorption spectrometry : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy at Massey University
    (Massey University, 1993) Guo, Xun
    Methods of solvent extraction have been developed for the determination of gallium, indium, and thallium in meteorites and other geological materials. The extraction of gallium is based on forming a chloro complex in HCl solution and extraction into MIBK. Indium was extracted into the same solvent as an iodo complex in an HBr + KI medium to which KOH had been added. Thallium was also extracted as an iodo complex from a H2SO4 + KI medium with addition of K2HPO4 as a salting out agent. Serious interference from iron(III) was eliminated by adding KI to reduce this element to its divalent state that was not extractable into the organic phase. Graphite furnace atomic absorption spectrometric techniques were employed to determine these three elements in the MIBK phase after extraction from the aqueous phase. Very low limits of detection (l.o.d.) were obtained with these methods. It was possible to lower the l.o.d for these elements either by increasing the aqueous/organic phase ratio before extraction, or by multiple loading injections. Using the developed methodology, gallium, indium, and thallium were quantified in iron and chondritic meteorites as well as in Cretaceous/Tertiary boundary clays, and some volcanic emissions. The data for thallium abundances in 49 iron meteorites were the first ever recorded for this type of meteorite and allowed for taxonomic separation of the various groups of irons. Indium abundances were only recorded in six chondrites because of the very low concentrations in iron meteorites. My data for thallium and other elements were used to classify the previously non-studied Manitouwabing iron meteorite. All three Group IIIA elements were determined in Cretaceous/Tertiary boundary clays and it was shown that these and other chalcophile elements have an abundance greater than that which would have been expected from either a volcanic or impact-derived source. Possible sources of this enrichment are discussed.