Simple and sensitive determination of radium-226 in river water by single column-chromatographic separation coupled to SF-ICP-MS analysis in medium resolution mode

This article describes a novel and simple method to measure ultra-trace Ra-226 in river water samples at fg L-1 (mBq L-1) levels as a means for surveying Ra-226 in an unintended contamination in river water. To simplify the procedure, a single column was used for separation and purification; 10 mL of AG 50W-X8 resin was packed into a 10 mL Eppendorf pipette tip, which was used as a separation column. A 500 mL sample solution was loaded, and interfering elements were removed with 80 mL 4 M HCl in 20% ethanol. Subsequently, Ra together with Ba was eluted by 20 mL 5 M HNO3 prior to SF-ICP-MS analysis; this allows the naturally existing Ba in water samples to be employed as a yield tracer for Ra-226 analysis. Using the medium mode of SF-ICP-MS, the instrumental detection limit of 380 fg L-1 (10 mBq L-1) was obtained. An extremely low method detection limit of 0.46 fg L-1 (0.02 mBq L-1) was achieved with 500-fold pre-concentration. Finally, the developed technique was applied to analyze natural water samples collected from Japanese rivers, in which the Ra-226 concentrations varied in the range of 0.7-49.6 fg L-1 (0.03-1.82 mBq L-1).