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

Abstract

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 226Ra 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 226Ra signal were investigated. Results: Analyzing 12 replicates (water spiking at 22 fg g−1 of 226Ra), the 226Ra recovery efficiency close to 100 % has been obtained. The instrumental 226Ra 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 226Ra analysis by SF-ICP-MS. The improvements in the separation and pre-concentration techniques also helped to improve the 226Ra detection limit down to 0.05 fg/25 mL of groundwater sample.