High precision analysis of potassium stable isotopes using the collision/reaction cell Neoma MC-ICPMS/MS

Abstract

Potassium isotopes hold great promise for tracing geological processes, but their analyses are fraught with complexities. Various methods using different generations of MC-ICPMS instruments have been developed, each with distinct advantages and disadvantages. In this study, we report on K isotopic measurements performed using the Thermo Fisher Scientific Neoma collision cell MC-ICPMS/MS to explore the potential of the instrument. Tests were conducted under wet plasma conditions and the precision achieved was ∼0.03 to 0.1‰ (95% c.i.) for 5–25 measurements in a single analytical session, comparable to other established techniques. The measurements were accurate within the tested concentration range of 50–500 ppb K. A K concentration mismatch between samples and standards of up to 5% was acceptable, while acid molarity mismatch had a pronounced effect on the measured K isotopic compositions. Matrix elements did not significantly impact K isotopic measurements when their concentration was below 2% of K. Several geostandards were measured and the obtained values agree with those from other measurement techniques. Overall, our tests suggest that measuring K isotopes with Neoma collision cell MC-ICPMS/MS is possible, but the high sensitivity of the instrument to tuning settings requires considerable efforts for conducting such measurements.