HR: 0800h
AN: V51B-0571    [Abstracts]
TI: Isotopic Measurement of Lead in Nanogram Quantities on Multi-Collector Inductively Coupled Plasma Mass Spectrometry
AU: * Lo, Y
EM: r95224101@ntu.edu.tw
AF: Yun-Chieh Lo, No. 1, Sec. 4, Roosevelt Road, Dept. Geosciences, National Taiwan University, Taipei, 10617, Taiwan
AU: Shen, C
EM: river@ntu.edu.tw
AF: Yun-Chieh Lo, No. 1, Sec. 4, Roosevelt Road, Dept. Geosciences, National Taiwan University, Taipei, 10617, Taiwan
AU: Gallet, S
EM: gallet@ntu.edu.tw
AB: Lead isotopes have been used as geochemical tracers in Earth Sciences, such as geochemistry, paleoclimatology and chronology, due to the diverse ratios and variable elemental abundance. Determination of Pb isotope ratios, with 2-sigma external precisions of 200 ppm for ²⁰⁷Pb/²⁰⁶Pb and ²⁰⁸Pb/²⁰⁶Pb and 800 ppm for for ²⁰⁶Pb/²⁰⁴Pb, can be performed with a Faraday-cup protocol in static mode on a multi-collector ICP-MS (MC-ICP-MS), Thermo Electron Neptune. The sample size is as low as 3 ng of Pb consumed per measurement. Lead blanks, from acid, labware, and airborne particulate, was effectively reduced to less than 10 pg, which causes an isotopic ratio bias of 30-50 ppm at most. Isobaric interference of ²⁰⁴Hg on ²⁰⁴Pb was corrected by monitoring the ion beam intensity of ²⁰²Hg. Mass dependant instrumental fractionation was normalized to ²⁰⁵Tl/²⁰³Tl value. A desolvation nebulization system, Cetac Aridus, and an X-skimmer cone were used to enhance signal intensity. With a sample uptake rate of 50 μ L/min, Pb concentration of 5-10 ng/ml offers an ion beam intensity of larger than 1 volt for ²⁰⁸Pb. The measured isotope ratios with 2-sigma external uncertainty of an international standard of NIST- Pb 981 are: ²⁰⁶Pb/²⁰⁴Pb= 16.9419 ± 0.012, ²⁰⁷Pb/²⁰⁶Pb= 0.91475 ± 0.0002 and ²⁰⁸Pb/²⁰⁶Pb= 2.1674 ± 0.00035. The key merit of this technique is to provide a possibility of analyzing Pb isotopic composition in trace-quantity of 1-10 ng, mainly for sample with limited Pb content.
DE: 0454 Isotopic composition and chemistry (1041, 4870)
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting