Determination of113mCd in natural water

A method has been developed for the determination of^113mCd from fallout in large-volume environmental water samples. In the analytical procedure a known amount of cadmium carrier is added to the sample and the cadmium is preconcentrated as insoluble hydroxide by coprecipitation with ferric hydroxide. The separated cadmium is purified from other interfering elements by an anion—exchange procedure. Finally, cadmium is coprecipitated with copper sulfide, and the radioactivity of^113mCd is measured in a lowbackground, gas-flow proportional beta counter. The cadmium recovery is established by determining the amount of Cd in the precipitate using an energy dispersive x-ray fluorescence spectrometer. For a 24hr counting period a lower limit of detection around 50μBq^113mCd/1 of sample has been attained. Samples of Lake Michigan water were analyzed: the concentration of^113mCd in 1980 was 177±5 μBq/l.