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

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: Ge-74/Ge-70, Ge-73/Ge-70 and Ge-72/Ge-70. The isotope ratio repeatability of a mono-elemental solution relative to another mono-elemental solution is better than 0.06parts per thousand per u at 95% confidence. Variations in sample Ge-74/Ge-70, Ge-73/Ge-70, and Ge-72/Ge-70 ratios are expressed as delta(74)Ge delta(73)Ge and delta(72)Ge units, respectively, which are deviations in parts per 10(3) 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 4.4parts per thousand decrease of delta(74)Ge. 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.