Determination of Six Heavy Metal Elements in Soil by Inductively Coupled Plasma Atomic Emission Spectrometry after Microwave Digestion with Four Acids

A method for the determination of six heavy metal elements in soil by ICP-AES after microwave digestion with four acids was established. 0.10-0.20 g of soil samples were wetted with a small amount of water, added with 6 mL of nitric acid, 2 mL of hydrochloric acid, 1 mL of hydrofluoric acid and 1 mL of 30% (mass fraction) hydrogen peroxide solution. The mixture was kept under steady condition for 15 min to make it to fully react, and placed in a microwave digestion apparatus for digestion according to the temperature program. The digestion solution was heated on a hot plate at 140 ℃ until the solution was nearly dry. The residue was dissolved and diluted to 25 mL with 1% (volume fraction) nitric acid solution, and detected under the optimized ICP-AES conditions. The selected analytical spectral lines of Pb, As, Ni, Cu, Zn and Cr were 220.353, 189.042, 231.604, 327.396, 213.856, 267.716 nm, respectively. The results showed that the mass concentrations of the six elements within 1.00 mg·L^-1 (for Pb, As, Cu, Ni) and 2.00 mg·L^-1 (for Cr, Zn) were linearly related to the corresponding spectral response values, with detection limits (3s) in the range of 0.29-5.76 μg·L^-1. The standard sample was analyzed 6 times repeatedly by the proposed method, giving RSDs of the determined values in the range of 0.60%-2.6%, and the determined values were basically consistent with the certified values.