Quantification of Ra at environmental relevant levels in natural waters by ICP-MS: Optimization, validation and limitations of an extraction and preconcentration approach.

Radium (Ra) at environmental relevant levels in natural waters was determined by ICP-MS after an off-line pre-concentration procedure. The latter consisted of Ra selective elution from potential interfering elements (i.e. other alkaline earth cations: Ba, Sr, Ca, Mg) on a series of two different ion exchange resins (AG50W-X8 and Sr-resin). The overall analytical method was optimized according to the instrumental performance, the volume of water sample loaded on resins, and the sample salinity. Longer acquisition time (up to 150 s) was required to ensure stable measurement of Ra by ICP-MS at ultra trace level (1.0pgL). For a synthetic groundwater spiked with Ra at 10.0pgL, the analytical procedure demonstrated efficient separation of the analyte from its potential interfering elements and a complete recovery, independent of the sample volume tested from 10 up to 100mL. For synthetic seawater spiked at a level of 10.0pgL of Ra, the total load of salts on the two resins should not exceed 0.35g in order to ensure a complete separation and recovery of Ra. The method was validated on natural waters (i.e. groundwater, freshwater and seawater samples) spiked with Ra at different levels (0.0, 0.5, 1.0 and 5.0pgL). Absolute Ra detection limits were determined at 0.020pgL (0.73mBqL) and 0.12pgL (4.4mBqL) respectively for 60.0mL of freshwater sample and for 10.0mL of seawater.