Accurate determination of arsenic and selenium in plant food samples by using ICP-MS/MS

Abstract

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.