Low-level 226Ra determination in groundwater by SF-ICP-MS: optimization of separation and pre-concentration methods

Background Inductively coupled plasma mass spectrometry (ICP-MS) techniques have been widely used for analysis of long-lived environmental radionuclides. In this paper, we present an optimization of the sector field (SF)-ICP-MS technique for the analysis of 226 Ra in groundwater samples using a method of pre-concentration of radium in water samples. Methods The separation protocol and a sequential application of ion exchange and extraction chromatography have been optimized, and related polyatomic interferences and matrix effects affecting the 226 Ra signal were investigated. Results Analyzing 12 replicates (water spiking at 22 fg g −1 of 226 Ra), the 226 Ra recovery efficiency close to 100 % has been obtained. The instrumental 226 Ra detection limit of 0.09 fg g −1 (3σ criterion) and the absolute detection limit of 0.05 fg in a 25-mL groundwater sample have been reached. Conclusions An optimization of the radium separation method and a pre-concentration of radium in groundwater samples led to high radium recoveries, almost up to 100 %. The same could be said with respect to the separation of the interfering elements, important for the quantitative 226 Ra analysis by SF-ICP-MS. The improvements in the separation and pre-concentration techniques also helped to improve the 226 Ra detection limit down to 0.05 fg/25 mL of groundwater sample.