During the STROMASS MSCI project, ultralow level Sr-90 determination was attempted using inductively coupled plasma mass spectrometry instruments. The ultralow level means femto-gramm (fg) range, which is 10-15 g. At this level, the main challenge of the analytical method is to minimize the isobar mass interference from the Zr-90. Zr has five isotopes and mass 90 is the most abundant one with 51.5 % abundance.
In this work, at first, direct Sr-90 determination was attempted with a direct analytical approach using a laser ablation system (Cetac Teledyne Analyte Excite Excimer) connected to an inductively coupled plasma mass spectrometer (ICP-MS) (Agilent 8800). The Agilent 8800 is a triple quadrupole instrument mounted with two quadrupole mass analyser and a collision/reaction cell. Using the oxygen gas in the reaction cell, the Zr-90 can be removed. However, the performed efficiency of the Zr-90 removal (99.7 %) was not enough to accomplish direct analysis with laser ablation. Therefore, a separation process that removes Zr from Sr cannot be skipped.
To remove Zr-90, extraction chromatography separation was applied. In this way, the efficiency of the Zr-90 removal was better than 99.99 %.
Another important parameter for ultralow level Sr-90 determination is to produce an ion beam with higher intensity. For this purpose, a desolving nebulizer system (Teledyne CETAC Aridus II) was used. Comparing this nebulizer system to pump-aspirated ordinary glass, quartz, and inert PFA nebulizers, a 7–10 times stronger ion beam was produced.
Using the triple quadrupole ICP-MS (Agilent 8800) with desolving nebulizer system, Sr90 was detectable at the level of 1 fg/g (5 mBq/g).
In the meantime, a second-generation triple quadrupole ICP-MS (Agilent 8900) that has increased sensitivity is made available on the market.
Because there is currently no research institute in Slovenia that has this instrument, new collaboration with experts from the Ruđer Bošković Institute in Zagreb, Croatia was established, to test developed analytical approach on the enhanced triple quadrupole ICP-MS.
Using the second-generation triple quadrupole ICP-MS (Agilent 8900) with desolving nebulizer system, Sr-90 is detectable at the level of 0.1 fg/g (0.5 mBq/g). In practice, this means that Sr-90 is measurable at the level of 10-16 g, which is quite a unique performance.
The mass spectrometry method introduced here can give a new direction to radionuclide analysis in a nuclear emergency since a rapid Sr-90 analysis can be accomplished in environmental, biological or food sample amounts of 1 g or less. Minimized sample size allows for speeding up the sample preparation and Sr separation procedure and using the advantage of the short analysis time of the mass spectrometry method, analysing hundreds of samples in a limited timescale.
Furthermore, because the sample preparation and Sr separation procedures do not need the use of strong acids or radioactive tracers, these steps can be done in any laboratory equipped with a furnace and hot plate.
Another advantage of the MS method is that other beta particle emitter fission products released in a nuclear accident, such as Cs, Te, Sn isotopes, Y-90, Sr-89, and so on, have no interference with Sr-90.
The disadvantage of this procedure is that Zr contamination must be regularly monitored and verified in sample vials, containers, and acids used for analyte production.
The findings of the study have been disseminated by presentations at a total of nine scientific conferences, comprising six international conferences and three domestic conferences held in Hungary. Additionally, two informative presentation materials were prepared and presented and subsequently delivered to the general audience in various Slovenian and Hungarian forums.
