Isotope ratio measurement by hexapole ICP-MS: mass bias effect, precision and accuracy

Isotope ratios were measured from the low mass (Mg-25/Mg-26) to the high mass (Tl-203/Tl-205) 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 Mg-25/Mg-26 to 0.7% for Tl-203/Tl-205, 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 H-2) 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 Sri standard spiked with Sn-117-enriched spike. The overall precision was found to be 0.1-0.6% relative standard deviation.