Eliminating Mo isobaric interference using O2 as reaction gas for Tc measurement by triple quadrupole ICP-MS

Abstract

Monitoring of ultra-trace level ⁹⁹Tc in environmental samples is important for radioactivity assessment and tracing oceanographic processes. ⁹⁷Tc is an ideal yield tracer for the analysis of ⁹⁹Tc. However, when using ⁹⁷Tc as the tracer for ⁹⁹Tc measurement in environmental samples, complex and tedious chemical separation procedures were needed for the separation of isobaric interference of ⁹⁷Mo. In this work, for the first time, we reported a method for the measurement of Tc isotopes by triple quadrupole ICP-MS (ICP-MS/MS). An APEX-Ω high efficiency sample introduction system was used for the improvement of the instrument sensitivity. The absolute detection limit for ⁹⁹Tc was estimated to be 0.9 fg (0.6 mBq). We introduced O₂ gas into the reaction cell of ICP-MS/MS. The majority of Mo⁺ reacted with O₂ to form MoO⁺ and MoO₂⁺ ions, which were eliminated by the second mass filter behind the reaction cell. A high separation factor (>1000) of Mo and Tc was found at an O₂ flow rate of 70%. By using this method, the effect of trace amounts of Mo in the sample solution on the measurement of Tc could be negligible.