Determination of Ultralow Level ¹³⁵Cs and ¹³⁵Cs/¹³⁷Cs Ratio in Environmental Samples by Chemical Separation and Triple Quadrupole ICP-MS

Abstract

An analytical method was developed for the determination of ultralow level 135 Cs in environmental samples by chromatographic separation of cesium with AMP-PAN and AG50W-X8 columns and sensitive measurement of cesium isotopes with triple quadrupole inductively coupled plasma mass spectrometry (ICP-MS/MS). Cesium was simply released by acid leaching using aqua regia from environmental solid samples and preconcentrated on AMP-PAN column. The cesium adsorbed on the column was effectively eluted with NH 4 Cl solution without dissolving the AMP. The excessive amount of NH 4 Cl in the eluate was removed by sublimation in the presence of small amount of LiCl. The remaining barium and other interfering elements such as Mo, Sn, Sb, and Li were efficiently removed using cation exchange chromatography (AG50W-X8). The decontamination factors of this procedure are above 4 × 10 7 for barium and 4 × 10 5 for molybdenum; the chemical yields of cesium are more than 85% for samples of less than 10 g. This method enables to separate cesium from large size of samples for the determination of ultralow level 135 Cs, avoiding the problem of removal of a huge amount of Mo in the dissolved AMP. Intrinsic 137 Cs in the environmental samples measured by gamma spectrometry before and after separation was used as internal isotope dilution standard for quantitative determination of 135 Cs without complete release and recover of radiocesium. The interference of barium ( 135 Ba and 137 Ba) to the ICP-MS measurement of 135 Cs and 137 Cs was further suppressed to 8 × 10 −5 by using N 2 O as the reaction gas in ICP-MS/MS at a flow rate of 0.7 mL/min, so a total suppression of 2 × 10 −12 for Ba was achieved, making the isobaric interference of Ba isotopes to the measurement of 135 Cs and 137 Cs in environmental samples negligible. A detection limit of 9.1 × 10 −17 g/g for 135 Cs and 137 Cs was achieved for 60 g samples. The developed method was validated by analysis of standard reference materials and successfully applied for the determination of 135 Cs concentrations and 135 Cs/ 137 Cs ratios in soil samples collected from Denmark, Sweden, and Ukraine. The 135 Cs/ 137 Cs isotopic ratios in Danish soil (2.08−2.68) were significantly higher than that from Sweden and Ukraine (0.65−0.71), indicating different sources of radiocesium. This work demonstrated the application of 135 Cs/ 137 Cs as a unique fingerprint for discriminating the sources of radioactive contamination and estimating their contribution to the total inventory, which will be useful for nuclear forensics and environmental tracer studies.

Trends and Advances in Inductively Coupled Plasma Tandem Quadruple Mass Spectrometry (ICP-QMS/QMS) With Reaction Cell

“…5, N2O, CO2, and CH4 were also used in multiple reports instead of the default cell gases. By using N2O as the cell gas, the production rate of the oxide ions of (Mn, Fe, Ni, Cu, Zn, and Se), 1 Sr, 3,68 Br, 8 Ba, 23 (Ge, Eu, Yb) 29 and Ra, 28,45 is greatly improved in comparison to those obtained by using O2 as the cell gas. This feature provides a higher sensitivity and/or a better separation of spectral interference.…”

“…Research fields and objectives. The research fields of the above references covered biology, 1-15 energy, 16 environment, 9,[17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32] food/medical, 10-12,25-27,33-40 geology, 28,41-47 material, [48][49][50][51][52][53][54][55][56][57][58][59][60] and radionulide, 4,[22][23][61][62][63][64][65][66][67][68][69][70][71] respectively. In addition to these conventional elemental analysis topics, a study on the gas phase catalytic reaction has also been reported by using the reaction cell of ICP-QMS/QMS as the in-situ reaction field.…”

“…Many references used He, H2, O2, or NH3, which are usually included as the default cell gas for ICP-QMS/QMS. 4,22,26,44,46,[62][63][64][65][66] There are also multiple references using N2O, 3,23,28,45,68 CO2, 24,27,65 or CH4 43 as the cell gas to improve the separation of spectral interferences. For single element solution, the typical relative uncertainty of isotopic ratio obtained by ICP-QMS/QMS is roughly in the range from 0.1% to 0.2%, which is inferior to that can be achieved by multiple collector (MC-) ICP-MS by 3 to 4 orders of magnitude.…”

“…3,28,45 On the other hand, highly precise analysis of the Cs isotopes ( 135 Cs + and 137 Cs + ) was achieved by complete conversion of the interfering ions, i.e., 135 Ba + and 137 Ba + , to oxide ions using N2O as the cell gas and resulted in the complete elimination of the spectral inteferences. 23,68 Regardless of the fact that CO2 as the cell gas did not improve the sensitivity for isotope analysis of U at the mass-shift mode by ICP-QMS/QMS, effective separation of the spectral interferences was achieved for the measurement of Pu + at the on-mass mode by improving the conversion of UH + to UO + . 24 Single particle analysis.…”

Developing Accelerator Mass Spectrometry Capabilities for Anthropogenic Radionuclide Analysis to Extend the Set of Oceanographic Tracers

“…The low abundance of 135 Cs with its high isobaric background of 135 Ba makes it difficult to detect, also for mass spectrometric approaches. Due to this difficulty, most studies presenting 135 Cs/ 137 Cs ratios were performed on water with 135,137 Cs/ 133 Cs ratios of 10 −8 or higher, i.e., close to sources of contamination (Zhu et al, 2020a). Two recent studies show first results on 135 Cs concentration in general seawater from the west coast of Greenland.…”