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variety of ways. These range from reductions in ionization efficiency within the plasma to the deposition of ion-beam inhibiting sample material (e.g., salts or metaloxides) in the interface region between the plasma source and mass spectrometer. Therefore, there are two sample dependent matrix effects which need to be addressed for routine geochemical analyses, one of which may suppress analyte intensities within an individual sample (e.g., ionization efficiency), and a second effect which may induce a time-dependent signal drift due to high TDS content in the samples. Correcting for these sample matrix effects is achieved by using internal standardization, in which all ICPMS solutions (blanks, external calibration standards, CRMs, and samples) are spiked with an equivalent amount of an internal standard. The applicability of this method is critically dependent upon the condition that the chosen internal standard must not be present in appreciable amounts in any of the ICPMS solutions (blanks, standards, or samples). For this purpose three elements are used for internal standardization following the methods of Doherty (1989); Ru, Re, and Bi. These three elements are ideal as they have low blank values for the reagents used in the decomposition and ICPMS methods, are present at very low concentrations in the majority of geological materials, produce no significant interference effects for the elements of interest, and are themselves free of significant interferences for their monitored isotopes ( 101 Ru, 187 Re, and 209 Bi). The default ICPMS analysis consists of running samples in small batches bracketed by calibration standards and blanks, and is described in Figure 3. A typical ICPMS analysis consists of four to six of these small sample batches run consecutively in a single day, and is called an ICPMS run. Prior to analysis, appropriate sample dilution factors are determined based upon the sample type, and samples are diluted either in 0.5 M HCl for HF-HClO 4 pressure decompositions, or in 0.5 M HNO 3 for carbonate decompositions. Acid and method blanks, calibration standards, as well as CRMs are diluted in the same acid matrix as the samples, and all solutions are spiked with 10 μg/kg of the Ru, Re, Bi internal standard. Matching the acid matrix of the samples and calibration standards is crucial, as calibration standards prepared in HNO 3 typically display ~10% greater instrument response than calibration standards prepared in HCl. While HNO 3 is more commonly used for preparation of ICPMS solutions as a result of this improved instrument response (as well as fewer interfering polyatomic species at low masses), it does not produce 11
Figure 3. Diagram depicting the order in which various blanks, calibrations standards, and samples are analyzed for a single ICPMS sample batch. A typical ICPMS analysis consists of four or more sample batches run consecutively. The acid blank refers to the 0.5 M HCl or HNO 3 acid matrix used for diluting all ICPMS solutions for a given analysis. Note that all solutions are spiked with 10 μg/kg of the internal standard, and that Ru, Re, and Bi in the second 10 μg/kg 32 element calibration standard within a batch are used for application of internal standard corrections for that batch. The certified reference material is a commercially available geostandard that is included within every sample decomposition and run repeatedly with every sample batch. See text for details. stable solutions with respect to high field strength elements (HFSE) such as Zr, Nb, Hf, and Ta (Münker, 1998), and therefore these elements are stabilized using trace amounts of HF in the stock 1 mg/kg calibration solutions. This stability issue for HFSE in dilute HNO 3 (0.5 M) means that samples processed using the carbonate decomposition method should be analyzed by ICPMS within 24 hours following completion of the sample decomposition. For samples processed using the HF-HClO 4 pressure decomposition and diluted in 0.5 M HCl, samples are also analyzed immediately, though this acid matrix appears sufficient for stabilizing HFSE on 12
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Iron sedimentation and the neodymiu
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The process(es) by which IFs were d
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This thesis represents original and
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viii
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goal of the research is to discern
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Figure 1. Map of southern Africa sh
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Page 18 and 19: 100 10 MORB 1 0.1 raw data (mg/kg)
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Page 42 and 43: Haley B.A., Klinkhammer G.P. (2003)
Page 44 and 45: Lee J.H. and Byrne R.H. (1993) Comp
Page 46 and 47: Piepgras D.J. and Wasserburg G.J. (
Page 48 and 49: Tosiani T., Loubet M., Viers J., Va
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Page 52 and 53: Abstract The benefits of inductivel
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Page 82 and 83: For the more recent, full 32 elemen
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Page 92 and 93: 1 IF-G/shale 0.1 0.01 La Ce Pr Nd P
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Page 112 and 113: Govindaraju K. (1995) 1995 working
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Appendix 1. Literature reference va
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Appendix 1 continued. Data in mg/kg
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the concentration of the major elem
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Potential interferences on monoisot
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1500 0.5 M HCl 4.0 interference on
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4000 0.40 0.20 3500 0.17 mg/kg 0.18
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interference on 95 Mo in sample sol
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Nd isotopes in 2.9 Ga Archean surfa
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Table 2 Trace element concentration
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Author's personal copy B.W. Alexand
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and preservation of oxide-facies IF
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TOP relative stratigraphic position
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The mechanism by which the alkali m
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6. Widdel, F. et al. Ferrous iron o
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82 PRESERVATION OF PRIMARY REE PATT
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ulk, open ocean seawater tended to
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