Determination of ultra-trace level 241Am in soil by triple-quadrupole inductively coupled plasma-mass spectrometry with mass-shift mode combined with chemical separation

Abstract

The interference of polyatomic ions from interfering elements (Pb, Hg, Tl, etc.) is an important factor that limits the use of inductively coupled plasma mass spectrometry (ICP-MS) in the measurement of ultra-trace level ²⁴¹Am in environmental samples. This study developed a novel analytical method to determine ultra-trace level ²⁴¹Am using ICP-MS with triple-quadrupole and collision-reaction gas (ICP-MS/MS). The interference of polyatomic ions from interfering elements was completely removed by the mass filter of the quadrupole and reactions with O₂, with the fake counts of interfering elements at m/z 257 or 259 (AmO⁺) lower than 0.01 cps and relatively high measurement sensitivity (1760 Mcps (mg L⁻¹)⁻¹). The detection limit of ²⁴¹Am was reduced to 0.017 fg g⁻¹ (corresponding to 0.0022 mBq g⁻¹). Based on the chemical reaction of O₂ and collision focusing (and buffering) of the He gas flow, the Am sensitivity is improved and the interference of polyatomic ions from interfering elements (Pb, Hg and Tl) can be completely eliminated whether Cl⁻ is present in the sample solution or not. The developed method was validated with a certified reference material of soil and also successfully verified with deep-layer soils with a low concentration of ²⁴¹Am.