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

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).