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

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.

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

“…The filament was cooled to room temperature and set in the TIMS apparatus with the vacuum reduced to 3 × 10 −7 mbar. The filament was preheated under a 1500 mA current ramped at 1500 mA min −1 , which was maintained for one hour to remove the organic content 18 in TIMS instrument. Prior to TIMS measurements, the current was raised at 100 mA min −1 until the 86 Sr intensity reached 6 V. The temperature was increased to 1640 °C (approximately 1 h integration).…”

“…18,19 The dark noise, which ranged from 0.009 to 0.012 cps at m/z = 89.8927, was corrected along with the peak tail derived from 88 Sr in the sample. 18 To avoid isobaric interference of trace amounts of 90 Zr impurity in the Re laments, the laments were baked in a lament-baking apparatus and were discarded if their m/z = 89.8927 noise exceeded 0.04 cps. 19 To prepare a natural Sr solution, strontium carbonate (Fujilm Wako Pure Chemicals Co., Ltd, Osaka, Japan) was dissolved in 0.100 M HNO 3 and then diluted to 10.0 ng mL −1 Sr (natural) with 0.100 M HNO 3 .…”

“…BEW ) calculated by eqn (3) from the apparent amount of 90 Sr (W app.Sr-90 ) calculated by eqn (2):18 …”

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

“…, thermal ionization mass spectrometry). 16 Apart from chemical separation, O 2 has been introduced via a dynamic reaction cell after mass filtering in conventional studies and via a collision/reaction cell (CRC) between two mass filters in recent studies, resulting in ion-molecule reactions to mitigate the polyatomic and isobaric interferences ( e.g. , 90 Zr + , 89 YH + ) for the 90 Sr measurement by ICP-MS. 17–20 The present challenges in the measurement of 90 Sr by ICP-MS are: (1) polyatomic interferences due to oxides ( e.g.…”

“…Therefore, inductively coupled plasma mass spectrometry (ICP-MS) has been attempted as an alternative method to measure 90 Sr for rapid emergency response with less cost compared to other mass spectrometric techniques (e.g., thermal ionization mass spectrometry). 16 Apart from chemical separation, O 2 has been introduced via a dynamic reaction cell aer mass ltering in conventional studies and via a collision/reaction cell (CRC) between two mass lters in recent studies, resulting in ion-molecule reactions to mitigate the polyatomic and isobaric interferences (e.g., 90 Zr + , 89 YH + ) for the 90 Sr measurement by ICP-MS. [17][18][19][20] The present challenges in the measurement of 90 Sr by ICP-MS are: (1) polyatomic interferences due to oxides (e.g., 72 Ge 18 O + and 74 Ge 16 O + ) become serious aer O 2 introduction (Table S2 †); 20,21 (2) the sensitivity of ICP-MS is lower than those with conventional radiometric methods, resulting in a relatively high method detection limit (MDL) even when using large samples, for example, approximately 1 Bq per sample using 1.2-1.6 L of synthetic urine samples; 19 and (3) it would be difficult to collect large volume samples (e.g., 1 L) from members of the public in the case of a large-scale RN accident.…”