226Ra determination in Japanese river waters by sector field ICP-MS

Radium-226 (226Ra,T1/2 = 1600 y) is a naturally occurring radioisotope belonging to the 238U decay series. It is the predominant radionuclide brought to the surface with water during crude oil extraction as well as being present in various radioactive wastes associated with past uranium processing. Due to its high specific activity (3.7x10e10 Bq g-1) and long biological half-life in bones (16400 y), 226Ra draws much attention as one of the most toxic natural radionuclides. 226Ra enters the human body mainly through drinking water, thus, monitoring of 226Ra in environmental waters is an important task.We describe a chemical separation procedure for the determination of 226Ra in river water samples with sector field ICP-MS (SF-ICP-MS). The proposed procedure is based on the combination of ion-exchange and extraction chromatography for preconcentration and separation of Ra from aqueous samples. The Diphonix ion-exchange resin has been used for extracting alkali earth cations from natural water samples. This extraction is followed by the separation of Ba(Ra) from major (Ca, Mg, Na, K) and trace (Sr, Pb, W, Mo etc.) elements on the Muromac resin. Quantitative elution of Ba(Ra) from the resin is achieved using semi-concentrated HNO3. Final separation of Ra from Ba is performed by the selective retention of Ba on the Sr-Spec extraction chromatographic resin. With a pre-concentration factor of 200, overall chemical recovery for Ra is found to be over 95% by the developed procedure. We show that capability of SF-ICP-MS is sufficient for 226Ra determination in natural water after the selective extraction of the analyte. The method is applied to the analysis of 226Ra in 10 river water samples collected allover Japan. Measured 226Ra concentration ranges from 0.23 -1.25 mBq L-1 with average of 0.55 mBq L-1.10th Triennial International Symposium on Mass Spectrometr