Direct quantification of femtogram per liter (fg L^-1) level ⁹⁰Sr in rainwater using thermal ionization mass spectrometry

Thermal ionization mass spectrometry (TIMS) is a specialized technique that precisely measures isotopicratios. This paper proposes the direct quantification of90Sr at femtogram per litter (fg L-1) levels us ingisotope dilution (ID)-TIMS of preconcentrated samples. Although preconcentration is ineffective when measuring isotope ratios in classical TIMS, the magnification afforded by preconcentration improves the limit of detection (LOD) of90Sr in ID-TIMS. After fixing the isotope ratio between stable Sr isotopes and90Sr, the fg L-1-level90Sr concentration was successfully obtained by the ID method (recovery R%=100 +/- 11.1%). The obtained LODs are improved by 10(5) times from those of conventional radiometric analysis such as oxalic acid precipitation/low background gas flow counters, which depend on the amount of coexisting natural Sr. Under the optimized conditions, the LOD was 9.03 attograms per liter (ag L-1),equivalent to a radioactivity concentration of 46.1 micro becquerels per liter (m Bq L-1). The sample volume (10 mL containing 10mgL(-1)of natural Sr) roughly corresponds to a rainwater-level sample with10(4)-fold preconcentration. Spike and recovery tests were conducted on rain water and related environmental waters (stagnant stock water collected from a swimming pool immediately after the Fukushima Daiichi Nuclear Power Plant accident). The90Sr levels were successfully quantified by the proposed method