An improved method for the rapid determination of ⁹⁰Sr in cow's milk

An improved method was developed to rapidly determine strontium-90 (⁹⁰Sr) in cow's milk samples in the event of a nuclear emergency. To perform this method, no heating or ashing steps were needed and all of the material used was disposable. Stable Sr tracer was added to each 40 mL milk sample. Hydrochloric acid (HCl) and trichloroacetic acid (TCA) were added to the sample to flocculate the suspended fat and proteins in the milk. The sample was centrifuged and the strontium in the supernatant was precipitated with carbonate. The resulting precipitate was dissolved in 8 M HNO₃ and the solution was passed through a Sr resin to remove potential interferents. Strontium was eluted from the resin using a small volume of water. Strontium-90 was measured by liquid-scintillation counting (LSC) and the tracer by inductively coupled plasma mass spectrometry (ICP-MS). The figures of merit of the method were determined and the method was validated using spiked samples.