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

Abstract

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.

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

“…In particular, the BGN ( m / z 90) is relatively high when the RPQ lens is not used (yellow circles in Figure ). This relatively high BGN is caused by the peak tailing of 88 Sr, which has the highest natural isotopic abundance of 82.58%. , Relatively, the use of the RPQ lens lowered the BGN ( m / z 90) by a factor of 6.7 (orange circles in Figure ), resulting in an intensity of 0.009 ± 0.001 cps (as opposed to c.f. 0.641 ± 0.172 cps without the RPQ).…”

“…2.1 × 10 −1021 and 2.7 × 10 −1223 ) were obtained by increasing the amount of stable Sr on the filament (100 ng of Sr in the previous literature). 23 Thus, the concentration of stable Sr in the actual sample must be known (using other instrumental analyses) before the TIMS measurement, and preparation to achieve constant amounts (appropriate amounts) of stable Sr on the filament is essential. However, doping of the filament with sufficient amounts of stable Sr results in a significant increase in the BGN at m/z 90, as detected by an electron multiplier (EM).…”

“…The previously reported dark noise measurements obtained using RPQ revealed consistently low values. 23 In this method, the measurement conditions were fixed except for natural Sr amounts (W n(Sr-88) ); thus, W BEW was determined by W n(Sr-88) .…”

“…Conversely, thermal ionization MS (TIMS) is capable of satisfying both the measurement of highly precise isotope ratios and microdroplet samples. − Studies have shown that the ID–total evaporation (TE)–TIMS technique (ID–TE–TIMS) is capable of quantifying 90 Sr directly via the determination of natural Sr in a sample. This technique exhibits high analytical repeatability and high quantitative capability without the need to chemically separate Zr, which causes isobaric interference of 90 Zr to 90 Sr .…”

“…Consequently, relatively low and highly precise isotope ratios of 90 Sr/ 88 Sr (cf. 2.1 × 10 –10 and 2.7 × 10 –12 ) were obtained by increasing the amount of stable Sr on the filament (100 ng of Sr in the previous literature) . Thus, the concentration of stable Sr in the actual sample must be known (using other instrumental analyses) before the TIMS measurement, and preparation to achieve constant amounts (appropriate amounts) of stable Sr on the filament is essential.…”