This method is used to estimate organic-complexed Fe and Al from soils by extracting with a 0.1M sodium pyrophosphate solution. The extraction solution only slightly dissolves noncrystalline inorganic forms and does not attack silicate minerals and crystalline Fe and Al oxides and hydroxides. Fe and Al are quantitated by ICP-OES. The method has detection limits of approximately 20 ppm for Fe and Al.
Ross, G. J. and Wang C. 1993. Extractable Al, Fe, Mn, and Si. pp.239-246. In: Carter, M. R. (ed), Soil Sampling and Methods of Analysis, Canadian Society of Soil Science, Lewis Publishers, Ann Arbor, MI.