Determination of soil organic aluminum extracted 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 described. 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 atomic absorption spectrophotometry. The difference between the two extractants was assumed to be organic Al. The CuCl2 solution extracted more Al than the KCI solution, and the difference increased with increasing soil organic carbon. The Al concentration in soil extracts measured by FISE and by atomic absorption spectrophotometry was about the same with advantages in automatization and safety. The interference by Cu2+ 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 adapted 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 carbon and less than 7 mu mol L-1 of total Fe.