DETERMINATION OF SOIL ORGANIC ALUMINUM EX TRACTED BY CUCL2

A potenciometric method for the determination of Al with fluoride ion selective electrode (FISE) in 0.5 mol L-1 CuCl2 soil extract is descri bed. The experiment was performed in Londrina, State of Parana, using synthetic solutions and soil extracts. Aluminum was extracted by CuCl2 and KCI solutions, and determined by potenciometry with FISE and by a tomic absorption spectrophotometry. The difference between the two ext ractants was assumed to be organic Al. The CuCl2 solution extracted mo re Al than the KCI solution, and the difference increased with increas ing soil organic carbon. The Al concentration in soil extracts measure d by FISE and by atomic absorption spectrophotometry was about the sam e with advantages in automatization and safety. The interference by Cu 2+ in the FISE determination was masked by the addition of 0.2g L-1 of o-phenantroline. The FISE-Al method is rapid, sensitive, easily adapt ed for routine and was realiable when tested in soils containing from 16 to 352 mmol kg(-1) of Al, from 0.8 to 125.0 g kg(-1) of organic car bon and less than 7 mu mol L-1 of total Fe.