Accurate determination of arsenic and selenium in plant food samples by using ICP-MS/MS†
Arsenic (As) and selenium (Se) in food have caused public concern. Determination of As and Se in plant food samples encounters mass spectral interferences. The influence of polyatomic and doubly charged ions on the determination was evaluated by monitoring 75As, 77Se, 78Se, 80Se, and 82Se in four modes. The result showed that serious interferences were observed by using “no gas” mode (octopole vented, single quadrupole mode). Most but not all interferences could be removed when using He mode (He used as the collision gas, single quadrupole mode) or H2 mode (H2 used as the reaction gas, MS/MS mode), while O2 mass-shift mode (O2 used as the reaction gas, MS/MS mode) enabled the effective removal of all interferences. In the O2 mass-shift mode configuration, the ions of interest were filtered twice by using the mass-to-charge ratio, enabling the removal of all interfering species. As and Se concentrations could be determined interference-free by using mass-shift mode with O2 as reaction gas. The performance of O2 mass-shift mode was investigated for the determination of As and Se in five plant reference materials. The obtained results were consistent with the certified values, indicating that the O2 mass-shift mode was an effective method to determine As and Se in plant food samples. The detection limits of the method for 75As, 77Se, 78Se, 80Se, and 82Se were 0.5, 0.7, 1.1, 0.3 and 0.6 ng g−1, respectively.