Precise isotopic determination of Hf and Pb at sub-nano gram levels by MC-ICP-MS employing a newly designed sample cone and a pre-amplifier with a 1012 ohm register

Abstract

Precise isotopic determination methods for Hf and Pb at sub-nano gram levels have been undertaken for this contribution utilizing the Neptune multiple collector ICP-MS (MC-ICP-MS) with a newly designed sample cone (the Jet cone) and a new pre-amplifier with a highly-resistive register of 10¹² ohm. The Jet cone enhanced sensitivities 1.6 and 3 times for Hf and Pb, respectively. The Jet cone showed no significant improvements in reproducibility of Hf isotope analysis at >1 ng compared to the normal cone, but the reproducibility improved considerably by half when Hf concentration of <1 ng was measured. Thus, 0.3 and 0.8 ng of Hf can yield reproducibility (2SD in ε-unit) of 3 and 1.7, respectively. Reproducibility (RSD) of ²⁰⁷Pb/²⁰⁶Pb, ²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb and ²⁰⁸Pb/²⁰⁴Pb were 0.026, 0.28, 0.33 and 0.36% using total Pb of 0.025 ng, and 0.02, 0.10, 0.10 and 0.08% using 0.05 ng, respectively. Thus, the Jet cone with the new pre-amplifier showed the best performance compared to the normal cone and pre-amplifier and are similar or even better than those obtained by the ²⁰²Pb-²⁰⁵Pb double-spike TIMS or multi-ion counting ICP-MS techniques.