Determination of Eight Heavy Metal Elements in Soil by Microwave Digestion- Inductively Coupled Plasma Atomic Emission Spectrometry

Soil was sampled by quartering, air-dried and pulverized to pass through sample sieve with bore diameter of 0.149 mm. A portion (0.200 0 g) of the soil sample was taken and digested in a microwave digester with a selected acid mixture of 6 mL of HNO₃ and 2 mL each of HCl and HF, under programmed temperature elevation. The digested solution was removed to an acid expeller and evaporated to 2-3 mL at 170℃. There are some black residues remaind insoluble in the solution, the evaporation should repeated by heating at 180℃ with an addition of 3 mL of HClO₄ to have the sample dissolved completely. The solution was concentrated to a syrupy consistency and after cooling, its volume was made up to 25.0 mL with HNO₃ (1+99) solution. The solution was mixed thoroughly and use for ICP-AES determination of 8 heavy metal elements, i.e., Co, Cr, Cu, Ni, Mn, Pb, V and Zn. Linear relationships between values of mass concentrations of the 8 elements and their signal intensities were found in definite ranges. Values of detection limits (3s) were found in the range of 0.3-6.6 μg·L^-1, and RSDs (n=6) of the measured value were all less than 2%.