COMPARISON OF CHELATING-AGENTS AS EXTRACTANTS FOR METALS IN DIVERSE SOIL MATERIALS

Five chelating agents-DTPA, EDTA, EGTA, HEDTA, and NTA - were compared at pH 5. 3 as extractants for Al, Fe, Mn, Zn, Cu, Cd, and Ni in 25 diverse soils. Extracting solutions contained 0. 005M chelating agent, 0. 01M CaCl//2, and 0. 1M acetic acid-ammonium acetate buffer at pH 5. 3. These extractants were compared to: a similar solution without added chelating agent, 0. 1M HCl, and the DTPA soil testing solution (0. 005M DTPA, 0. 01M CaCl//2, buffered at pH 7. 3 by 0. 1M triethanolamine). All extractants yielded clear filtrates that aspirated and burned cleanly during analysis by flame atomic absorption spectrometry. At the 5:1 extractant/soil ratio used, all buffered extractants maintained their pH satisfactorily.