Multiple Daly Isotope Measurements on the Nu Plasma 3 MC-ICP-MS

Abstract:

One of the latest developments on the Nu Plasma 3 MC-ICP-MS is the incorporation of multiple Daly detectors among a suite of Faraday detectors, enabling simultaneous measurements of multiple low-abundance isotopes in addition to higher abundance isotopes. Daly detectors offer significant advantages over the Secondary Electron Multiplier (SEM) type ion counters: a larger dynamic range providing better overlap with the Faraday, better gain stability, excellent linearity across a larger count range, and a longer life time. The Jackson School of Geosciences at the University of Texas at Austin has one of the first Nu Plasma 3 with a collector housing including 6 Dalys and 16 Faradays, designed to facilitate multi-Daly analysis of Pb, U and Th isotopes.

In this study, Pb solutions were used to calibrate the Daly-Faraday gains to ensure measurement accuracy and reproducibility and to determine accurate deadtime corrections for each Daly to ensure consistent ratios, independent of solution concentration. Eleven measurements of solutions of SRM981, alternating between three different concentrations (0.4 ppb, 0.2 ppb and 0.1 ppb) yielded Daly/Daly ratios with reproducibility of ~0.2% 2SD and Faraday/Daly ratios with reproducibility of ~0.15% 2SD.

Lead solution multi-Daly work has characterized multi-Daly behaviour in preparation for U and Th isotope analyses for U-Th geochronology and ocean anoxia studies and is the first step in developing multi-Daly laser ablation techniques.