Abstract

Isotope ratios were measured from the low mass (²⁵Mg/²⁶Mg) to the high mass (²⁰³Tl/²⁰⁵Tl) region, using an ELAN 5000 and a Platform Hex-ICP-MS, to investigate mass bias effects on the two instruments. For the ELAN 5000, the percentage mass discrimination per atomic mass unit (MD%) varies from 5% for ²⁵Mg/²⁶Mg to 0.7% for ²⁰³Tl/²⁰⁵Tl, whereas for the Platform it ranges from 10% to 0.11%, respectively. The Platform has higher mass bias at low mass and lower mass bias at the high mass region compared to the ELAN 5000. The difference in mass bias between the two instruments is attributed to the different ion transferring lens system, i.e., electrostatic lens system in the ELAN 5000 and hexapole collision cell in the Platform. For the Platform Hex-ICP-MS, the addition and variation of collision/reaction gases (He and H₂) does not introduce any additional mass bias. The precision and accuracy of isotope ratio measurement by the Platform Hex-ICP-MS were assessed using the NBS982 Pb isotope reference material and an elemental Sn standard spiked with ¹¹⁷Sn-enriched spike. The overall precision was found to be 0.1–0.6% relative standard deviation.