Rapid Simultaneous Determination of ²³⁷Np, ^239-241Pu and ²⁴¹Am in Water Samples

In nuclear emergency, it is crucial to quick assess the level and extent of radioactive contamination. Highly toxic transuranic nuclides (²³⁷Np, ^239-241Pu and ²⁴¹Am) are the most important radionuclides in radioactive contamination. In the case for analysis of multiple radionuclides in the same sample, the reported analytical methods are often time-consuming/tedious by using multiple chromatographic separation resins for the separation of every single radionuclide. In this work, a rapid analytical method for simultaneously determining transuranium nuclides in water samples was developed by coupling triple quadrupole inductively coupled plasma mass spectrometry (ICP-MS/MS) with a single DGA resin column, Np, Pu, and Am were simultaneously enriched and purified. For monitoring chemical yields of Np/Pu and Am, the chemical recoveries are greater than 80% which is monitored using ²⁴²Pu and ²⁴³Am as tracers. O₂ was used as reaction gas in the collision reaction cell (CRC) of ICP-MS/MS, the chemical reaction behavior of Np and Pu with O₂ is similar, and Np/Pu reacts with O₂ and converts to \mathrmNpO_2^+ /\mathrmPuO_2^+ , and Am reacts with O₂ and concerts to AmO⁺. ²³⁷Np, ^239-241Pu and ²⁴¹Am in the same solution were simultaneously measured by the He-O₂ mode of ICP-MS/MS in the same run, and the cross contamination of ²⁴¹Pu and ²⁴¹Am (＜1%) was achieved using 8.0 mL/min He-0.37 mL/min O₂ as reaction gas. A sensitivity of 814×10⁶ s⁻¹/(mg/L) for Np, 799×10⁶ s⁻¹/(mg/L) for Pu, and 1 027×10⁶ s⁻¹/(mg/L) for Am is achieved, and the sensitivity ratio of \mathrmNpO_2^+ and \mathrmPuO_2^+ is close to 1, indicating that ²⁴²Pu is feasible as a non-isotope tracer of Np under this condition. The abundance sensitivity of U and the interference of polyatomic ions (¹H²³⁸U⁺, ¹H₂²³⁸U⁺, ²⁰⁶Pb³⁵Cl⁺, ²⁰⁴Pb³⁷Cl⁺, ²⁰⁴Hg³⁷Cl⁺, ²⁰⁵Tl³⁶Ar⁺ and ^209\mathrmBi^16\mathrmO_2^+) formed by U and matrix elements (Pb, Hg, Tl and Bi) are effectively inhibited. The detection limit (DL) of 1.84 fg/L for ²³⁷Np, 2.08 fg/L for ²³⁹Pu, 0.70 fg/L for ²⁴⁰Pu, 0.66 fg/L for ²⁴¹Pu and 1.27 fg/L for ²⁴¹Am are approached, this is three orders of magnitude lower than the DL required in nuclear emergency situations (1 Bq/L). The developed method is validated by analyzing the spiked samples, and allows for the rapid, simultaneous detection of ultra-trace amounts of Np, Pu and Am in environmental water samples within 2.5 h. This significantly reduces analysis time and meets the requirement for emergency preparedness.