Precise determination of low abundance isotopes (¹⁷⁴Hf, ¹⁸⁰W and ¹⁹⁰Pt) in terrestrial materials and meteorites using multiple collector ICP-MS equipped with 10¹²Ω Faraday amplifiers

Analytical protocols for measurements of isotope ratios involving low-abundance isotopes ¹⁷⁴Hf (~0.16%), ¹⁸⁰W (~0.12%), and ¹⁹⁰Pt (~0.014%) using multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) at ca. tenfold improved precision compared to previous studies are presented. The improvements in precision result in part from the use of Faraday amplifiers equipped with 10¹²Ω resistors for collection of the isotope beams of interest, as well as for the isotope beams used to monitor isobaric interferences. For ion currents >5×10^-13 A (>50mV on an amplifier with 10¹¹Ω resistor), uncertainties (2s.d.) of better than 100ppm are typically achieved for isotope ratios involving ¹⁷⁴Hf, ¹⁸⁰W and ¹⁹⁰Pt. Terrestrial isotope abundances (atomic percent ±2s.d.) of ¹⁷⁴Hf (0.16106±0.00006; n=15); ¹⁸⁰W (0.11910±0.00009; n=10); and ¹⁹⁰Pt (0.01286±0.00005; n=9) were determined on reference solutions throughout multiple analytical sessions over ~3years. The results, however, rely on the accuracy of the reference value chosen for the isotope ratios employed for mass bias correction and, to a lesser extent, on the accuracy of the exponential mass fractionation law used for mass bias correction. For the precise determination of isotope ratios involving ¹⁷⁴Hf, ¹⁸⁰W and ¹⁹⁰Pt in natural materials, efficient chromatographic separation schemes for Hf and W from silicate-rich matrices, and for Pt from iron meteorite matrices, are presented that provide effective separation of the element of interest from interfering elements. First results for Pt suggest that IAB, IIAB and IIIAB iron meteorites exhibit terrestrial ¹⁹⁰Pt abundances within uncertainty. Three chondrite samples exhibit indistinguishable ¹⁷⁴Hf from terrestrial Hf. The isotope abundance of ¹⁸⁰W in meteorites is more variable due to radiogenic ¹⁸⁰W that was produced by ¹⁸⁴Os-decay.