Online solid-phase extraction-inductively coupled plasma-quadrupole mass spectrometric quantification of ⁹⁰Sr using...

Due to the lack of a correlation with the natural Strontium (Sr) isotopes, it is difficult to apply the isotope dilution (ID) method to an artificial radioactive mononuclide Strontium-90 (⁹⁰Sr), in inductively coupled plasma-quadrupole mass spectrometry (ICP-QMS). Meanwhile, online solid-phase extraction (SPE)-ICP-QMS (SPE-ICP-QMS) serves as an automatic sequential analytical technique for measuring the ultra-trace amounts of radionuclides; however, apparent assay values obtained using this method are often negatively affected by differences in the sample matrix composition between standard and actual samples. In this study, the pg L^-1 level of ⁹⁰Sr was successfully measured by combining online SPE-ICP-QMS and the ID method with ⁸⁸Sr/⁸⁶Sr ratios in one sample injection, without the radioactive standard. Although naturally occurring abundant isobaric ⁹⁰Zr significantly influences ⁹⁰Sr quantification during mass spectrometry, consecutive separations between automated SPE and dynamic reaction cell (DRC) oxidation enable ⁹⁰Sr quantification, even in the presence of isobaric ⁹⁰Zr (acceptable down to 5.7 × 10^-9 of ⁹⁰Sr/Zr in sample solution), using this method. Through this method, both radioactive ⁹⁰Sr and naturally occurring Sr were simultaneously quantified using ⁸⁸Sr-to-⁸⁶Sr and ⁸⁸Sr-to-⁹⁰Sr ratios without radioactive ⁹⁰Sr standard solutions. This simultaneous quantification of stable Sr and ⁹⁰Sr was achieved within 15 min with good recovery rates. The limit of detection of ⁹⁰Sr was 1.1 pg L^-1 (equivalent to radioactivity 5.6 Bq L^-1) for a 10 mL injection. Finally, water collected from an actual contaminated water storage tank at the Fukushima Daiichi Nuclear Power Plant (Fukushima, Japan) was analyzed using the proposed method, and the obtained results agreed well with those obtained using conventional analytical methods.