Resolving the Germanium Atomic Weight Disparity Using Multicollector ICPMS

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Abstract
Two most recent mass spectrometric measurements of natural isotopic composition germanium gave discordant Ge atomic weight values of 72.6276(64)k=2 and 72.6390(69)k=2, respectively, a decade ago. Each measurement was performed with a different mass spectrometry platform, gas source isotope ratio mass spectrometry and thermal ionization mass spectrometry, respectively. Herein we report results obtained by multicollector inductively coupled plasma mass spectrometry yielding an atomic weight of germanium 72.6296(19)k=2 which is in support of the upcoming 2009 Standard Atomic Weight adjustment by IUPAC. Germanium isotope ratios were calibrated using a regression mass bias correction model and NIST SRM 994 gallium isotopic reference material. In this model, no assumptions are made regarding the mass bias differences between gallium and germanium or between the isotopes of germanium. Isotope ratios of 0.5620(21), 0.7515(16), 0.2125(7), and 0.2121(12) were obtained for n(70Ge)/n(74Ge), n(72Ge)/n(74Ge), n(73Ge)/n(74Ge), and n(76Ge)/n(74Ge), respectively, with expanded uncertainties (k = 2) estimated in accordance with the ISO/BIPM Guide to the Expression of Uncertainty in Measurements.