High precision measurement of germanium isotope ratio variations by multiple collector-inductively coupled plasma mass spectrometry

Abstract

Multicollector ICP-MS is used for the precise measurement of variations in the isotopic composition of germanium. Argon-based spectral interferences are assessed in the germanium mass region and the repeatability of the following ratios is determined: ⁷⁴Ge/⁷⁰Ge, ⁷³Ge/⁷⁰Ge and ⁷²Ge/⁷⁰Ge. The isotope ratio repeatability of a mono-elemental solution relative to another mono-elemental solution is better than 0.06‰ per u at 95% confidence. Variations in sample ⁷⁴Ge/⁷⁰Ge, ⁷³Ge/⁷⁰Ge, and ⁷²Ge/⁷⁰Ge ratios are expressed as δ⁷⁴Ge δ⁷³Ge and δ⁷²Ge units, respectively, which are deviations in parts per 10³ from the same ratio in the standard solution. The addition of sodium and potassium to a standard solution of germanium having a known isotopic composition induces up to 4.4‰ decrease of δ⁷⁴Ge. This chemical bias is a result of a mass-dependent process and prevents the measurement of natural samples without chemical separation. Germanium is quantitatively separated from alkali matrix using liquid chromatography techniques.