A Highly Sensitive Zirconium Hydrogen Phosphate Emitter for Ni Isotope Determination Using Thermal Ionization Mass Spectrometry

Abstract

The nickel isotope has a great potential for investigating biogeochemical processes in the geosciences and has been proven to be extremely useful for studying the chronology of the early solar system. As one of the most powerful techniques in metal isotopic ratio measurements, thermal ionization mass spectrometry (TIMS) shows poor sensitivity for Ni isotope ratio analysis, because the high ionization potential (7.640eV) of Ni makes it difficult to be ionized on a hot filament. In previous studies, a minimum of 1000 ng Ni was required using the classical Sigel-H3BO3-Al emitter or the Sigel-H3PO4-Al emitter. The present study is first to employ a highly sensitive zirconium hydrogen phosphate (Zr(HPO4)2) emitter to measure the Ni isotopes with TIMS. This emitter produces a significant enhancement in the ionization efficiency of Ni and enables the analysis of the Ni isotope at the 200 ng level with high precision. In addition, this newly developed emitter shows a strong inhibition to the Fe and Zn signals, which are the main potential isobaric interferences during Ni measurement. A series of analyses of the NIST SRM 986 standard demonstrated that an internal precision (2 RSE) of ± 0.03 to 0.05 ‰ can be achieved depending on the sample size. Analysis of the NIST SRM 986 standard also shows an external reproducibility (2 RSD, n = 10) of better than ± 0.11‰, even for Ni at 200 ng.