90Sr bioassay in small-volume urine by ICP-MS/MS with CO2 as the reaction gas†

It is critical to perform dose assessment after internal contamination with beta-particle emitting ⁹⁰Sr due to its relatively long physical and biological half-lives, along with the higher specific activities of ⁹⁰Sr and its daughter ⁹⁰Y. For rapid public screening after a large-scale radiological/nuclear accident, we developed a novel ⁹⁰Sr bioassay for small-volume urine samples using triple-quadrupole inductively coupled plasma-mass spectrometry (ICP-MS/MS). After organic matter decomposition of 10 mL urine using HNO_3, stacked DGA and Sr resin cartridges were used directly for chromatographic separation and purification of Sr. Yields of Sr were measured as 94 ± 5% (n = 12) for the whole procedure, using stable ⁸⁸Sr originally in the urine sample as a yield tracer. CO₂ proved to be a better reaction gas than O₂, to overcome isobaric/polyatomic interferences, especially those caused by Zr and Ge. With a conventional introduction system + s lens + 75% CO₂ flow rate in the 4^# cell gas line, the method detection limit (MDL) was estimated to be 0.978 pg L⁻¹ (5 Bq L⁻¹) in 10 mL urine, meeting the public screening requirement for judging ingestion/inhalation exposure beyond 1 mSv Committed Effective Dose Equivalent, with a reasonable throughput (∼6 h for 12 samples). For method validation, the standard reference materials provided by PROCORAD (Association for the PROmotion of Quality COntrol in RADiotoxicological Analysis), France, were analyzed and the results were all in good agreement with the assigned values.