Eliminating Mo isobaric interference using O-2 as reaction gas for Tc measurement by triple quadrupole ICP-MS

Monitoring of ultra-trace level Tc-99 in environmental samples is important for radioactivity assessment and tracing oceanographic processes. Tc-97 is an ideal yield tracer for the analysis of Tc-99. However, when using Tc-97 as the tracer for Tc-99 measurement in environmental samples, complex and tedious chemical separation procedures were needed for the separation of isobaric interference of Mo-97. 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-omega high efficiency sample introduction system was used for the improvement of the instrument sensitivity. The absolute detection limit for Tc-99 was estimated to be 0.9 fg (0.6 mBq). We introduced O-2 gas into the reaction cell of ICP-MS/MS. The majority of Mo+ reacted with O-2 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 O-2 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.