Triple-Quadrupole Inductively Coupled Plasma-Mass Spectrometry with a High-Efficiency Sample Introduction System for Ultratrace Determination of ¹³⁵Cs and ¹³⁷Cs in Environmental Samples at Femtogram Levels

Abstract

High yield fission products, (135)Cs and (137)Cs, have entered the environment as a result of anthropogenic nuclear activities. Analytical methods for ultratrace measurement of (135)Cs and (137)Cs are required for environmental geochemical and nuclear forensics studies. Here we report a highly sensitive method combining a desolvation sample introduction system (APEX-Q) with triple-quadrupole inductively coupled plasma mass spectrometry (AEPX-ICPMS/MS) for the determination of (135)Cs and (135)Cs/(137)Cs isotope ratio at femtogram levels. Using this system, we introduced only selected ions into the collision/reaction cell to react with N2O, significantly reducing the isobaric interferences ((135)Ba(+) and (137)Ba(+)) and polyatomic interferences ((95,97)Mo(40)Ar(+), (119)Sn(16)O(+), and (121)Sb(16)O(+)). Compared to the instrument setup of ICPMS/MS, the APEX-ICPMS/MS enables a 10-fold sensitivity increase. In addition, an effective chemical separation scheme consisting of ammonium molybdophosphate (AMP) Cs-selective adsorption and two-stage ion-exchange chromatographic separation was developed to remove major matrix and interfering elements from environmental samples (10-40 g). This separation method showed high decontamination factors (10(4)-10(7)) for major matrix elements (Al, Ca, K, Mg, Na, and Si) and interfering elements (Ba, Mo, Sb, and Sn). The high sensitivity of APEX-ICPMS/MS and the effective removal sample matrix allowed reliable analysis of (135)Cs and (137)Cs with extremely low detection limits (0.002 pg mL(-1), corresponding to 0.006 Bq mL(-1) (137)Cs). The accuracy and applicability of the APEX-ICPMS/MS method was validated by analysis of seven standard reference materials (soils, sediment, and plants). For the first time, ultratrace determination of (135)Cs and (135)Cs/(137)Cs isotope ratio at global fallout source environmental samples was achieved with the ICPMS technique.

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

“…In addition, the AMP-PAN column can efficiently remove Ba, Sb, and Sn by factors of 7300, 20, and 1400, respectively, which are much better than that using AMP powder. 14 This is very critical to achieve a better separation of Cs from Ba and other interfering elements in a large size soil or sediment samples (e.g., 60 g) for ultralow-level 135 4 Cl was sublimated at a temperature of above 350°C for more than 2 h. However, it was observed that most of cesium (>60%) was (Table 1).…”

“…The overall decontamination factors of 4 × 10 7 for Ba, 4 × 10 6 for Li, 4 × 10 5 for Mo, 3 × 10 5 for Sn, and 2 × 10 5 for Sb were achieved, which are better or comparable compared to the reported values using combined chromatographic purification (AMP-PAN, AGMP-1 M, and AG 50W-X8). 14,18 In consideration of all steps including ICP-MS measurement, the entire analysis of a batch of 8 samples can be completed within 3 days. The overall chemical yields of 135 Cs were measured by counting the 137 Cs in the original samples and the final separated cesium solution by gamma spectrometry to be more than 85% for soils from Sweden and Ukraine.…”

“…For 60 g of soil sample, the detection limit of the method for 135 Cs and 137 Cs can be calculated to be 9.1 × 10 −17 g/g (or 0.30 mBq/g for 137 Cs and 3.9 nBq/g for 135 Cs) considering a recovery of 65% for cesium and 2 mL final solution prepared for measurement; this value is more than 1 order of magnitude better than the reported value using ICP-MS/MS. 14 Validation of the Developed Method. There is no standard reference material of similar matrix as soil and sediment with certified for 135 137 Cs was measured in the soil collected from Gavle, Sweden and 142− 286 Bq/kg in Feofaniya, Ukraine, they are 1−3 orders of magnitude higher than the level in the soil received only global fallout.…”

“…Mass spectrometry is therefore a practical technique for 135 Cs measurement in the environmental samples. Among them, resonance ionization mass spectrometry (RIMS), thermal ionization mass spectrometry (TIMS), − sector field inductively coupled plasma-mass spectrometry (SF-ICP-MS), , electric thermal vaporization ICP-MS (ETV-ICP-MS), and triple quadrupole inductively coupled plasma mass spectrometry (ICP-MS/MS) − have been used for this purpose. ICP-MS/MS is becoming the most attractive mass spectrometric technique for the measurement of 135 Cs due to its highest popularity, high abundance sensitivity, and excellent removal of barium interference by reaction cell technique.…”

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

“…In this context, marine water materials certified for their 137 Cs content, e.g., IAEA 381 and 443 (Irish Sea Water), would be of specific interest, but are presently not on stock at IAEA. Irish sea sediment (IAEA-385; reference date for decay correction: 2019-01-01) with a certified 137 Cs activity of (19.8 ± 0.6) Bq/kg and a weighted mean of reported 135 Cs/ 137 Cs ratios of (1.15 ± 0.11) (Yang et al, 2016b;Zheng et al, 2016;Zhu et al, 2020a) thus presently seems to be the most suitable natural reference material for the advancement of Cs isotope measurements in the marine environment. In literature, we hardly find studies on 137 Cs in coral cores, which reflects the inefficient incorporation of Cs in the coral skeleton.…”