Abstract: Digesting sludge and soil samples by refluxing procedure with aqua-regia can extract to of heavy metals more tha n that by ordinary aqua-regia digestion.The present experiment investigated digestion procedure with nitric-perchloric acid(1:1)using an aluminium digestion block.A range of 128 siudge-treated soil samples were analyzed for seven elements: Cd,Cr,Cu,Pb,M n,Ni,Zn,and results have been compared with aqua-regia.The correlation coefficients imply clearly that the two digestion methods have a close correlation but the T tests denote that they give significant results.Except Zn,the extracting coefficients for these elements are obviously higher than those by using refluxing procedure with aqua-regia.Also,seven elements:Na,K,Mg,Ca,Mt,,Al,Fe,as potential interferences and different flames have been studied in the determination of Cr.The result showed that using fuel-lean dinitrogen oxide-acetylene flame would not produce neither positive nor negative interferences.

Key words: AAS, Heavy metals, Sludge