Rapid and Simultaneous Determination of ²³⁸Pu, ²³⁹Pu, ²⁴⁰Pu, and ²⁴¹Pu in Samples with High-Level Uranium Using ICP-MS/MS and Extraction Chromatography

As the most important plutonium isotopes, ²³⁸Pu, ²³⁹Pu, ²⁴⁰Pu, and ²⁴¹Pu are normally measured by two to three techniques, which are tedious, time-consuming, and not suitable for rapid analysis in emergency situations. Recently, ICP-MS has become a competitive technique for the rapid measurement of ²³⁹Pu, ²⁴⁰Pu, and ²⁴¹Pu. However, ICP-MS is difficult to measure ²³⁸Pu due to the serious isobaric interference of ²³⁸U. This work reports a rapid analytical method to solve this problem for the simultaneous determination of ²³⁸Pu, ²³⁹Pu, ²⁴⁰Pu, and ²⁴¹Pu using triple-quadrupole inductively coupled plasma mass spectrometry (ICP-MS/MS) combined with chemical separation. Chemical separation achieved a high decontamination factor of 2.12 × 10⁹ for the most critical interfering element, uranium, by using two sequential TK200 columns. The interferences of ²³⁸U¹H⁺ and ²³⁸U⁺ were effectively eliminated by using 12 mL/min He-6 mL/min NH₃ as the reaction gases in the octupole collision/reaction cell in ICP-MS/MS. Combined with chemical separation, the overall elimination efficiency of ²³⁸U¹H⁺ reached 3.6 × 10¹⁷, which is 10⁵ times better than the reported method. With the high ²³⁸U⁺ elimination efficiency of 1.12 × 10⁴ in the ICP-MS/MS measurement, the overall removal efficiency of ²³⁸U⁺ reached 10¹³, guaranteeing accurate determination of femtogram-level ²³⁸Pu as well as ²³⁹Pu, ²⁴⁰Pu, and ²⁴¹Pu in the samples containing milligram-level ²³⁸U. The detection time is reduced to minutes, well fulfilling the requirement of rapid analysis. This method is validated by analyzing the standard reference material and the spiked samples.