High-precision measurement of calcium isotopes in carbonates and related materials by multiple collector inductively coupled plasma mass spectrometry (MC-ICP-MS)

Abstract

Multi-collector ICP-MS has been used for the precise measurement of natural variations in the isotopic composition of Ca. The interference of Ar in the Ca mass region is assessed and the repeatability of the ⁴⁴Ca/⁴²Ca ratio of a sample calcium solution relative to the National Institute of Standards and Technology (NIST) Standard Reference Material (SRM) 915a Calcium Carbonate (Clinical) standard is better than 0.1‰ at 95% confidence. Variations in sample ⁴⁴Ca/⁴²Ca ratio are expressed as δ⁴⁴Ca units, which are deviations in parts per 10³ from the same ratio in the NIST SRM 915a Ca standard. Measurements of δ⁴⁴Ca are presented for terrestrial and marine carbonates, which show a variation of up to 0.7‰, in agreement with previous studies by thermal ionisation mass spectrometry (TIMS).