Introduction: Inductively coupled plasma mass spectrometry (ICP-MS) has been used for the determination of many radioisotopes including 99Tc, 226Ra, 235,236,238U, 232Th, and 239,240Pu. The major challenge in the determination of 90Sr is the separation of isobaric and polyatomic interferences. 90Sr is found in the environment at specific activities ranging from a few millibecquerels to several becquerels, depending on the medium studied. These specific activities, converted to masses, represent only a few femtograms and are significantly lower than the typical detection limits of most ICP-MSs using direct aspiration nebulization. This suggests that a pre-concentration of the 90Sr is necessary in order to increase the number of atoms detected. Objectives: The objective of this study was to develop a method for the ultratrace determination of 90Sr in environmental soil samples using ICP-MS. Methodology: Strontium was separated from matrix using a selective extraction chromatographic Sr-resin (100-150 m) from EiChrom. The resin was conditioned with 10 mL of 8 M HNO3. The samples were loaded and the resin was rinsed with 3 mL of 3 M HNO3. Zirconium and other matrix elements were washed from the column to leave pure Sr on the column. Strontium was eluted with 10 mL of distilled water. The final solution was analyzed by ICP-MS. Results: Following the acid digestion, extraction chromatography was tested to assess their usefulness in reducing its interferences. A 90Sr pre-concentration of >300-fold and recoveries of 60-70% were obtained using a combined extraction chromatography and pre-concentration by evaporation protocol. Improvement in sensitivity of 90Sr was found by optimization of the ICP-MS parameters using the stable isotope 88Sr. The detection limit was improved by a factor of 300 for 90Sr. A detection limit of 0.2 ppt was obtained. The method was applied to determine 90Sr in the environmental soil samples. The average 90Sr/86Sr isotope ratio was 4.05×10−9. Conclusions: The main 90Sr/86Sr isotope ratio in environmental soil samples confirms that the source of 90Sr is the global fallout. The overall time requirement for the measurement of 90Sr by ICP-MS is 2 days, significantly shorter than any radioanalytical protocol currently available.


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