High precision calcium isotope ratio measurements using a magnetic sector multiple collector inductively coupled plasma mass spectrometer

Abstract

Calcium isotope abundances were measured using a Finnigan Neptune magnetic sector multiple collector inductively coupled plasma mass spectrometer capable of resolving all molecular isobaric interferences from ⁴²Ca, ⁴³Ca, ⁴⁴Ca, ⁴⁶Ca and ⁴⁸Ca. Scattering events caused by the intense ⁴⁰Ar⁺ ion beam did not contribute to the uncertainty in the baseline of the calcium mass spectrum. Quantitative separation of the calcium from the sample matrix was carried out to ensure that the measurements were independent of the sample type. In addition, thorough desolvation of the aerosol was found to have a significant effect on the stability and sensitivity of the method. The stable mass bias of the instrument enabled normalization of the measured isotope abundance ratios relative to standard reference materials. Delta values including δ⁴⁴Ca/⁴³Ca, δ⁴⁴Ca/⁴²Ca and δ⁴⁸Ca/⁴²Ca were measured with external reproducibilities better than ±0.2‰ (2s) from 10 ppm solutions of calcium-containing materials, including sea-water and biogenic and non-biogenic marine carbonates.