Gd Matrix Effects on Eu Isotope Fractionation in Geological Rocks Using MC-ICP-MS: Optimizing Europium Isotope Ratio Measurements in Geological Samples

Eu has only two isotopes (151Eu and 153 Eu). Eu and Gd are one of the rare earth elements that are very difficult to completely separate from each other. Eu isotope ratio can be determined by MC-ICP-MS using internal Sm or Gd spikes to correct for mass discrimination. NIST3117a ultrapure chemical reagent shows almost no Eu isotope fractionation regardless of the kind of normalization isotope pair. However, Eu isotope ratio in the silicate rocks was effected by Gd matrix during MC-ICP-MS measurement if a trace amount of Gd impurity remains in the purified Eu fraction. In this report, we tried to determine optimizing conditions for precise and accurate Europium isotope ratio measurements in geological samples using MC-ICP-MS. The pure Eu fraction with almost no Gd matrix separated from geological samples and NIST3117a ultrapure chemical reagent show almost same degree of Eu isotope fractionation regardless of the kind of normalization isotope pair. However, Eu isotope ratio in the silicate rocks was effected by Gd matrix during MC-ICP-MS measurement using if 154 Gd interference relative to 154 Sm as internal standard is more than ca. 0.1%. Particularly, highly fractionated granite and high silica volcanic rock with extremely low Eu concentration compared to Gd require high – purity Eu separation with a high recovery rate to obtain the true value of the Eu isotope fractionation in the geological rocks.