Determination of Copper, Lead, Zinc, Cadmium and Chromium in Rice by Inductively Coupled Plasma Mass Spectrometry after Joint Digestion

The grinded sample (0.500 0-1.000 0 g) was added to 25 mL quartz beaker, soaked with 1 mL of nitric acid for 1 h, heated on the low temperature electric furnace to complete carbonization, and transfered to muffle furnace for ashing at 500℃ for 4 h. After cooling to room temperature, 4 mL of nitric acid (1+1) solution was added to dissolve the residue by heating at a low temperature, and the solution was made up to 25 mL with water for determination of copper, lead, zinc, cadmium and chromium by an inductively coupled plasma mass spectrometer. The salt and organic matter in the sample solution after ashing was greatly reduced, and the internal standard (¹⁰³Rh) correction eliminated the matrix effect and physical effect. The mathematics correction method was used to eliminate the interference of ¹¹⁴Sn on ¹¹⁴Cd, and the organic matter was removed by dry digestion to eliminate the interference of ⁴⁰Ar+¹²C on ⁵²Cr. Linear relationships were found between values of the response and mass concentration of copper, lead, zinc, cadmium and chromium in definite ranges, and the detection limits (3σ) were in the range of 0.005-0.44 μg·g^-1. Values of recovery obtained by standard addition method were in the range of 80.0%-125%, and RSDs (n=11) was less than 10%. The proposed method was used to determine the contents of copper, lead, zinc, cadmium and chromium in the national standard reference materials of rice, giving the measured values consistent with the certified values.