Determination of the Isotopic Composition of Gadolinium Using Multicollector Inductively Coupled Plasma Mass Spectrometry.

In this study, we report independent measurements of all stable isotope ratios of gadolinium. Our study employs multicollector inductively coupled plasma mass spectrometry (MC-ICPMS) with National Research Council Canada (NRC) HALF-1 isotopic hafnium standard as a primary calibrator and surveys four commercial gadolinium materials, including a NRC candidate isotopic reference material, GADS-1. The isotopic composition of gadolinium is determined using the regression model without reliance on conventional normalizing isotope ratios or mass-dependent isotope ratio correction models. In this work, all gadolinium isotope ratios were obtained from 160Gd/158Gd which, in turn, was measured from hafnium 178Hf/177Hf either directly or indirectly through 167Er/166Er. The latter approach was used for the final determination of gadolinium isotopic composition, as it provides smaller combined uncertainty. We report high-precision measurements of the isotopic composition of gadolinium, which support a revised standard atomic weight. Isotope amount ratios of R152/158 = 0.008 20(2)k=1, R154/158 = 0.087 98(12)k=1, R155/158 = 0.596 81(63)k=1, R156/158 = 0.825 08(57)k=1, R157/158 = 0.630 60(22)k=1, and R160/158 = 0.879 10(60)k=1, and the atomic weight of Ar(Gd) = 157.2502(6)k=1 were obtained for gadolinium in GADS-1.