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Characterization of Soil Humic Acids Extracted by Tributyl Phosphate
A procedure for extracting humic acid from soils using tributyl phosphate (TBP) is described. Humic acids were isolated from a cultivated Minnesota garden (MG) soil (Aquic Haploborolls) and the International Humic Substances Society (IHSS) reference soil (Aquic Haploborolls), and were characterized with respect to their elemental compositions, acidic functional group contents, and IR and C-13 NMR spectra. These characteristics are compared to those of the humic acids isolated from the same soils by the methylisoputyl ketone (MIBEK) method and traditional alkali extraction procedure. The effectiveness of TBP as an extraction solvent for humic acid was camparable to that of the traditional alkali extraction method. The TBP humic acid exhibited a lower N content, higher P content and higher acidic functional group content than either of the other two humic acids isolated from the same soil. Reasons for these differences are discussed.