HR: 0800h
AN: V51B-0567    [Abstracts]
TI: Fe Isotopic Analysis by a Nu Plasma 1700 MC-ICP-MS With a 58Fe-57Fe Double-spike
AU: * Konter, J G
EM: jkonter@projects.sdsu.edu
AF: SDSU, 5500 Campanile Dr, San Diego, Ca 92182,
AU: Pietruszka, A J
EM: apietruszka@geology.sdsu.edu
AF: SDSU, 5500 Campanile Dr, San Diego, Ca 92182,
AU: Hanan, B B
EM: bhanan@mail.sdsu.edu
AF: SDSU, 5500 Campanile Dr, San Diego, Ca 92182,
AB: High-resolution MC-ICP-MS is well suited for Fe isotope analyses in systems with small natural variations. In addition, the use of a double spike may improve reproducibility through precise correction of potential mass- dependent fractionation that may result from chemical separation of Fe using ion-exchange chromatography and from instrumental artifacts (e.g., mass bias and matrix effects). Therefore, we performed an error analysis to calculate theoretically attainable precision for both iterative and non-iterative approaches to data reduction and different double-spike compositions. We investigated a full range of double spikes with either a ⁵⁷Fe or ⁵⁴Fe spike mixed with a ⁵⁸Fe spike. Each double spike is theoretically mixed over the full range from pure double spike to pure standard and randomly fractionated simulating machine bias. For each mixture, we randomly perturb the input ratios one thousand times, at most by our in-run analytical errors. The standard deviation of a thousand differences with the true standard provides a precision estimate for each mixture. The results of this analysis show that the combination of an iterative procedure with a ⁵⁸Fe-⁵⁷Fe double spike has the potential for higher precision (to below 0.01 per mil) than a ⁵⁸Fe-⁵⁴Fe double spike. This lower limit is possible with our internal precision of 0.01 per mil (unspiked standard, 2SD) on the ⁵⁶Fe/⁵⁴Fe ratio. Such internal precision is not uncommon in other published data, however matrix effects and machine bias often degrade the external precision [e.g. Dideriksen et al., 2006]. Experiments with spiked solution standards and samples are required to determine if use of a ⁵⁸Fe-⁵⁷Fe double spike will translate into a significant improvement in the external precision of Fe isotope measurements using the Nu 1700 MC-ICP-MS.
DE: 1036 Magma chamber processes (3618)
DE: 1037 Magma genesis and partial melting (3619)
DE: 1041 Stable isotope geochemistry (0454, 4870)
DE: 1094 Instruments and techniques
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting