FAAS Determination of Metal Elements in Soil

The soil sample was digested with a mixed acid of HNO_3-HF-HClO_4(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 SiF_4↑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 Al~(3+) present in the sample and definite amount of SiO_3~(2-) remained,to the determination of Mn,definite amount of CaCl_2 solution was added as releasing agent to eliminate the interference.If relatively high content of iron was present in the sample,La(NO_3)_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 Pb~(2+) and Cd~(2+) 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.