High precision determination of 228Ra and 228Ra/226Ra isotope ratio in natural waters by MC-ICPMS

Abstract A new methodology has been developed for precise and accurate determination of 228 Ra and the radium isotope ratio ( 228 Ra/ 226 Ra) by multicollector inductively coupled plasma mass spectrometry (MC-ICPMS) in natural water. The method was tested on waters from Lake Kinneret (The Sea of Galilee) and saline springs that flow into it. The radium is pre-concentrated from 60 L of Lake Kinneret water (or 2 L of the saline springs water) by co-precipitation with MnO 2 . The separation of radium from the matrix elements was conducted by BioRad ® AG50W-X8 and Sr Spec ® resins. The instrumental limit of detection for 226 Ra and 228 Ra was 5 fg mL −1 (0.05 ppq) or 0.1 and 30 dpm L −1 , respectively, and the absolute limit of detection 0.005 fg. Internal precision of the radium isotope ratio ( 228 Ra/ 226 Ra) in Lake Kinneret for 228 Ra concentration as low as 0.10 fg L −1 (0.06 dpm L −1 ) was 2.8% (2 σ ) and external precision was 10% (2 σ , n  = 9).