Radium analysis by sector field ICP-MS in combination with the Diffusive Gradients in Thin Films (DGT) technique

Abstract

A new and simple method to assess low radium concentrations in water and sediment pore water was developed. The ²²⁶Ra ions are trapped on a laboratory prepared MnO₂ resin (3 other ones have also been tested) that is inserted in a DGT probe (diffusive gradients in thin films). The probe can be deployed for days to weeks sufficient to accumulate enough ²²⁶Ra to be quantified. Because the High Resolution ICP-MS was operated in low resolution mode to get the highest sensitivity, isobaric interference from the Sr88Ba138 molecular ion could not be avoided. However, the pre-concentration on the MnO₂ resin favours ²²⁶Ra accumulation versus that of Ba and Sr. The instrumental repeatability on a standard of 2 ng L⁻¹²²⁶Ra was 1.4% (n = 10), while the relative standard deviation on natural samples was 8% (average of 2.2 pg L⁻¹²²⁶Ra, n = 3). A detection limit as low as 0.022 pg L⁻¹²²⁶Ra (0.80 mBq L⁻¹) was achieved for a 24 h DGT deployment.