Simultaneous determination of femtogram levels of Np, Pu, and Pu in environmental solid samples using extraction chromatography and ICP-MS/MS.

An analytical method based on triple quadrupole inductively coupled plasma mass spectrometry (ICP-MS/MS) was developed for simultaneous determination of femtogram levels of Np, Pu, and Pu in environmental samples. By carefully controlling the valence states of Np and Pu in the entire separation procedure using a simple single extraction chromatographic column (TK200), the consistent behavior of Np and Pu was achieved, allowing for the reliable application of Pu as the chemical yield tracer for Np, Pu, and Pu. A high decontamination factor of 3.2 × 10 for the most critical interfering element, uranium, was achieved in the chemical separation step. The interferences of UH and peak tailing of U during the measurement of plutonium isotopes were effectively eliminated by utilizing 7.5 mL/min He-1.1 mL/min CO as reaction gases in the octupole collision/reaction cell and employing sequential quadrupole mode for mass separation in ICP-MS/MS. Specifically, the interference of UH was reduced to 10 and the peak tailing of U to 10, surpassing the performance of measurement method without reaction gases by 3 orders of magnitude. The developed method enables the accurate determination of femtogram levels of Np, Pu, and Pu in the samples with U/Np and U/Pu atom ratios of up to 10 and 10, respectively. The developed method was validated by analyzing standard reference materials and spiked soil samples.