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

A new methodology has been developed for precise and accurate determination of Ra-228 and the radium isotope ratio (Ra-228/Ra-226) 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 MnO2. The separation of radium from the matrix elements was conducted by BioRad (R) AG50W-X8 and Sr Spec (R) resins. The instrumental limit of detection for Ra-228 and Ra-228 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 (Ra-228/Ra-226) in Lake Kinneret for Ra-228 concentration as low as 0.10 fg L-1 (0.06 dpm L-1) was 2.8% (2 sigma) and external precision was 10% (2 sigma, n = 9). (C) 2010 Elsevier B.V. All rights reserved.