Removal of spectral interferences and accuracy monitoring of trace cadmium in feeds by dynamic reaction cell inductively coupled plasma mass spectrometry

In the direct ICP-MS determination of Cd in feed samples, significant spectral interferences caused by high concentrations of Mo can play an important role. In the present study, Mo based oxide or hydroxide polyatomic interferences were eliminated by dynamic reaction cell (DRC) with O₂ as reaction gas. Some other oxide or hydroxide interferences (i.e. Zr and Ru) were simultaneously reduced by this technology. These potentially interfering polyatomic ions ⁹⁵Mo¹⁶O⁺, ⁹⁴Mo¹⁶OH⁺, ⁹⁴Zr¹⁶OH⁺, ⁹⁸Mo¹⁶O⁺, ⁹⁸Ru¹⁶O⁺ and ⁹⁷Mo¹⁶OH⁺ on ¹¹¹Cd⁺ and ¹¹⁴Cd⁺ were oxidized to higher oxides MoO₂⁺, MoO₃⁺, MoO₄⁺, RuO₃⁺, RuO₄⁺, MoO₂H⁺, MoO₃H⁺, ZrO₂H⁺ and ZrO₃H⁺. The rejection parameter q (RPq) of DRC and the flow rate of O₂ were optimized and set at 0.75 and 2.0 ml min^{− 1}, respectively. In addition, the residual isobaric interference of ¹¹⁴Sn on ¹¹⁴Cd was corrected using a mathematical correction equation. The limit of quantitation (LOQ) for ¹¹¹Cd or ¹¹⁴Cd was 0.8 or 1.0 ng g^{− 1} and the analysis results of NIST 1567a wheat flour and 1568a rice flour standard reference materials were in good agreement with the certified values. As the routine cadmium monitoring method in our laboratory, the proposed method was applied to the accuracy determination of 562 pig feed samples for the Monitoring of Central Meat Reserves (CMR) of China.