Calcium isotope measurements using a collision cell (CC)-MC-ICP-MS

Calcium is a major element in terrestrial planets and has six stable isotopes, including 40Ca which is a product of radioactive decay of 40K (T1/2 = 1.25 Gyrs). Calcium isotope geochemistry has therefore been used to trace biological and geological processes in various environments as well as radiogenic dating. However, it has been technically impossible to analyze stable and radiogenic isotopes simultaneously and high precision measurements usually require tens of micrograms of Ca. Here, we present high-precision Ca isotopic data, including the stable isotopes 42Ca, 43Ca and 44Ca as well as the radiogenic 40Ca using a Nu Sapphire multi-collector inductively-coupled-plasma mass-spectrometer (MC-ICP-MS), that is equipped with a collision cell to minimize Ar based interferences. The stable isotopic variations are reported using the delta notation (δ40/44Ca, δ42/44Ca, δ43/44Ca), which is the permil deviation of a given ratio from the NIST SRM 915b standard. The radiogenic excess is reported as ε40Ca, the per ten thousand deviation of the 40Ca/44Ca ratio from the same standard, after internal normalization to the 42Ca/44Ca ratio. We tested the influence of various parameters (Ca concentration, Ca and HNO3 concentration mismatch between sample and standard, effect of matrix elements) on the precision and accuracy of the measurements. We show that, using ~ 100 ng is sufficient to obtain high precision (