Determination of low-level radiostrontium, with emphasis on in situ pre-concentration of Sr from large volume of freshwater sample using Powdex resin

An improved analytical method was developed for determining of low levels of radiostrontium in environmental freshwater samples. Emphasis was placed to the in situ pre-concentration of radiostrontium with Powdex resin in large volumes (100-300 L) of freshwater samples from many locations without using of deleterious substances such as NaOH and mineral acids. Measuring electric conductivity (EC) of water samples enabled the estimation of the amount of Powdex resin required for quantitative recovery of Sr from the large water samples in the field. The Powdex resin that adsorbed Sr was brought back to the laboratory, and Sr adsorbed in the resin was eluted by 8 M HNO3 together with Sr carrier added. Strontium was radiochemically separated by the cation exchange method for β counting after removal of most of the Ca using Ca(OH)2 precipitation. Through the procedure the Sr chemical yield was 88% on average. This analytical method was verified by analyzing 170 L of water samples with different salinity values, to which a known amount of 90Sr was added. The detection limits of 90Sr activities obtained using the 170 L water samples was estimated to be approximately 0.1 mBq L−1 for a counting time of 100 min. The method was also applied to environmental samples collected from Ibaraki and Fukushima prefectures; their 90Sr activities ranged from 0.16 to 0.93 mBq L−1.