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

Jo Aoki; Shigeyuki Wakaki; Hiroko Ishiniwa; Tomohiko Kawakami; Takashi Miyazaki; Katsuhiko Suzuki; Yoshitaka Takagai

doi:10.1021/acs.analchem.2c04844

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

Anal Chem. 2023 Mar 21;95(11):4932-4939. doi: 10.1021/acs.analchem.2c04844. Epub 2023 Mar 12.

Authors

Jo Aoki¹, Shigeyuki Wakaki², Hiroko Ishiniwa³, Tomohiko Kawakami⁴, Takashi Miyazaki⁵, Katsuhiko Suzuki⁵, Yoshitaka Takagai^{1

3}

Affiliations

¹ Faculty of Symbiotic Systems Science, Cluster of Science and Technology, Fukushima University, 1 Kanayagawa, Fukushima 960-1296, Japan.
² Kochi Institute for Core Sample Research, Japan Agency for Marine-Earth Science and Technology (JAMSTEC), 200 Monobe Otsu, Nankoku, Kochi 783-8502, Japan.
³ Institute of Environmental Radioactivity, Fukushima University, 1 Kanayagawa, Fukushima 960-1296 Japan.
⁴ Kaken Inc., 1044 Horimachi, Mito, Ibaraki 310-0903, Japan.
⁵ Japan Agency for Marine-Earth Science and Technology (JAMSTEC), 2-15 Natushima, Yokosuka, Kanagawa 237-0061, Japan.

PMID: 36906855
DOI: 10.1021/acs.analchem.2c04844

Abstract

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.