Determination of trace selenium in Ca-rich groundwater samples by ion molecule reaction ICP-MS and CH4 plasma modifier

- A method based on DRC-ICP-MS and addition of a CH4 plasma modifier was established.
- The 80Se+ was oxidized to 80Se16O+ by O2, and detected at m/z 96.
- 96Mo+ and 96Zr+ can be removed by oxidized to 96Mo16O+ and 96Zr16O+.
- The sensitivity of 80Se16O+ was increased 3.6-fold by introduced 2 mL min−1 CH4.

In this study, a reliable method based on the combination of ion molecule reaction ICP-MS and addition of a CH4 plasma modifier technique was established for the direct determination of Se in Ca-rich groundwater samples. The 80Se+ was oxidized to 80Se16O+ by O2, and detected at m/z 96. Under the optimized conditions (O2 flow rate = 0.6 mL min−1 and Rpq = 0.35), the new interferences of 96Mo+ and 96Zr+ could be oxidized to 96Mo16O+ and 96Zr16O+, and reduced by up to 300-fold and 457-fold. The poor sensitivity of 80Se16O+ was increased 3.6-fold by introduced 2 mL min−1 CH4 modifier to the ICP plasma. And a limit of quantification (LOQ, 10δ) of 0.06 μg L−1 was obtained. The accuracy of proposed method was validated by analysis of certified reference materials of trace elements in water (SRM 1643e) and trace elements in natural water (SRM 1640a), and the determined values were in good agreement with the certified values. The proposed method was also successfully applied for the determination of trace Se in Ca-rich groundwater samples, and the spiked recoveries was in the range of 90.0%-103%.

In order to eliminate the interference of 40Ca40Ar+, the 80Se+ was oxidized to 80Se16O+, and detected at m/z 96. The new interferences of 96Mo+ and 96Zr+ can be effectively removed by oxidized to 96Mo16O+ and 96Zr16O+.123