Simple Radiometric Determination of Strontium-90 in Seawater Using Measurement of Yttrium-90 Decay Time Following Iron-Barium Co-precipitation

Direct Quantification of Attogram Levels of Strontium-90 in Microscale Biosamples Using Isotope Dilution-Thermal Ionization Mass Spectrometry Assisted by Quadrupole Energy Filtering

Although thermal ionization mass spectrometry (TIMS) has been employed for the high-precision analysis of isotope ratios, direct quantification of artificial mono-nuclide in the environment is difficult by even using isotope dilution (ID) due to the coexistence of the great magnitude of natural stable nuclides or isobars. In traditional TIMS and ID-TIMS, a sufficient amount of stable Sr doped on a filament is required to realize a stable and adequate ion-beam intensity (i.e., thermally ionized beams). However, the background noise (BGN) at m/z 90, detected by an electron multiplier, disturbs ⁹⁰Sr analysis at low concentration levels due to peak tailing of a significant ⁸⁸Sr ion beam dependent on the ⁸⁸Sr-doping amount. Here, TIMS assisted by quadruple energy filtering was successfully employed for the direct quantification of attogram levels of an artificial monoisotopic radionuclide strontium-90 (⁹⁰Sr) in microscale biosamples. Direct quantification was achieved by integrating the ID quantification of natural Sr and simultaneous ⁹⁰Sr/⁸⁶Sr isotope ratio analysis. Additionally, the measurement amount calculated by the combination of the ID and intercalibration was corrected for the net result amount of ⁹⁰Sr by subtracting dark noise and the detected amount derived from the survived ⁸⁸Sr, which are equivalent with the BGN intensity at m/z 90. Background correction revealed that the detection limits were in the range of 6.15 × 10^-2-3.90 × 10^-1 ag (0.31-1.95 μBq), depending on the concentration of natural Sr in a 1 μL sample, and the quantification of 0.98 ag (5.0 μBq) of ⁹⁰Sr in 0-300 mg/L of natural Sr was successful. This method could analyze small sample quantities (1 μL), and the quantitative results were verified against authorized radiometric analysis techniques. Furthermore, the amount of ⁹⁰Sr in actual teeth was successfully quantified. This method will be a powerful tool for measuring ⁹⁰Sr in the measurement of micro-samples, which are required to assess and understand the degree of internal radiation exposure.

A part per trillion isotope ratio analysis of 90Sr/88Sr using energy-filtered thermal ionization mass spectrometry

Strontium-90 is a major radioactive nuclide released by nuclear accidents and discharge waste. Input of such radioactive nuclide into earth surface environment causes potential threat of long-term internal exposure when taken up by organism. Rapid and precise measurement of ⁹⁰Sr in variety of environmental sample is important to understand the distribution and dynamics of ⁹⁰Sr in the local environment after the accident and to assess the effect of radioactive nuclide inputs on bodies. However, previous ⁹⁰Sr measurement techniques have drawbacks such as long measurement times for radiometry and high detection limits for mass spectrometry. Here we present a technique to accurately measure a significantly small amount of ⁹⁰Sr in natural environmental samples using an energy-filtered thermal ionization mass spectrometry. Our technique achieved a ⁹⁰Sr detection limit of 0.23 ag, which corresponds to a ⁹⁰Sr activity of 1.2 µBq. The detection limit was lowered by two orders of magnitude compared with the previous mass spectrometric ⁹⁰Sr analyses. The ability of our technique will expand the applicability of mass spectrometric ⁹⁰Sr survey not only to the rapid ⁹⁰Sr survey upon nuclear accidents but also to study a long-term environmental diffusion of radioactive materials using size-limited environmental and biological samples.

Isotope Dilution-Total Evaporation-Thermal Ionization Mass Spectrometric Direct Determination of Radioactive Strontium-90 in Microdrop Samples

Thermal ionization mass spectrometry (TIMS) was used to directly quantify an ultratrace of radioactive ⁹⁰Sr in microliter droplet samples. No chemical separation was required in removing isobaric interferences on M = 90 such as ⁹⁰Zr and organic molecules in the mass spectrum because the difference in evaporation and ionization (emission) temperature among organic molecules, Zr and Sr, allows us to control the emission manner and significantly suppress the isobaric interferences. Direct quantification was achieved by improving the intercalibration of Faraday cups and ion counting in an isotope dilution (ID) method. Furthermore, the use of a total evaporation method (TE) enhanced the detection efficiency by the complete collection of the ⁹⁰Sr ion beam from the samples and minimized the complexity of the fractionation effect in the isotope ratio calculation. In this study, 1 fg of ⁹⁰Sr (equal to activity of 5 millibecquerel (mBq)) in a very low-volume sample with 10⁸ times greater isobaric interference from ⁹⁰Zr was successfully measured using the proposed ID-TE-TIMS method. The limit of detection was 0.029 fg (equal to 0.15 mBq) without any preconcentration. To demonstrate the wide usability of this method, low-volume samples of tears, eyelashes, saliva, environmental standards, and water samples (i.e., seawater and ground water) were analyzed within 1 h. The relationship of the measured values between this ID-TE-TIMS method and a radiometric analysis was shown to have good linearity.