Reduction of acid effects on trace element determination in food samples by CH4 mixed plasma-DRC-MS

A robust method for trace element determination in food samples by addition of methane to the plasma of a dynamic reaction cell mass spectrometer (CH4 mixed plasma-DRC-MS) was developed. Addition of 3 mL min−1 methane to Ar-plasma eliminates the signal suppressions of various elements (As, Se, Hg, etc.) due to the high concentration of nitric acid (10%, v/v). The CH4–Ar mixed plasma may compensate for the plasma cooling effects due to the highly concentrated nitric acid. The interfering polyatomic ions 40Ar12C+, 40Ar35Cl+ and 40Ar40Ar+ on 52Cr+, 75As+ and 80Se+ determination were removed effectively using the DRC with CH4 as the reaction gas. The limits of quantification (LOQ, 10σ) were 0.35 ng g−1, 0.07 ng g−1, 0.35 ng g−1, 0.07 ng g−1, 0.15 ng g−1, and 0.07 ng g−1 for As, Cd, Cr, Hg, Pb and Se, respectively. The proposed method was applied to the determination of these trace elements in four food standard reference materials (NIST1577b, GBW10018, NIST1570a and GBW10016), and the results were in good agreement with the certified values.