FAAS Determination of Metal Elements in Soil

The soil sample was digested with a mixed acid of HNO3-HF-HClO4 (5+5+3) and contents of Fe, Mn, Cu, Zn, Pb, Cd and Ni in the sample solution were determined separately by FAAS. Since most of the silicates in the sample were expelled as SiF4↑ during digestion, contents of Fe, Mn, Cu, Zn and Ni could be determined directly in the digested sample solution. Considering the negative interferences of Ti(Ⅳ) and Al3+ present in the sample and definite amount of SiO32- remained, to the determination of Mn, definite amount of CaCl2 solution was added as releasing agent to eliminate the interference. If relatively high content of iron was present in the sample, La(NO3)3 solution should be added to overcome its interference to the determination of Zn. In determination of Pb and Cd, separation by addition of KI solution to form anionic complexes with Pb2+ and Cd2+ and extraction of the complexes with MIBK were adopted and FAAS determination was done directly in the organic phase. Standard curves of the 7 elements were prepared by using the respective standard solutions, and linear regression equations with correlation coefficients from 0.999 2 to 0.999 6 were obtained. Test for recovery was made by standard addition method, values of recovery and RSD′s (n=6)found were in the ranges of 96.8%-99.9% and 0.9%-2.0% respectively.