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 th e Ca mass region is assessed and the repeatability of the Ca-44/Ca-42 ratio of a sample calcium solution relative to the National Institute of Standar ds and Technology (NIST) Standard Reference Material (SRM) 915a Calcium Car bonate (Clinical) standard is better than 0.1 parts per thousand at 95% con fidence. Variations in sample Ca-44/Ca-42 ratio are expressed as delta(44)C a units, which are deviations in parts per 10(3) from the same ratio in the NIST SRM 915a Ca standard. Measurements of delta(44)Ca are presented for t errestrial and marine carbonates, which show a variation of up to 0.7 parts per thousand, in agreement with previous studies by thermal ionisation mas s spectrometry (TIMS).