AN AUTOMATIC PROCEDURE FOR DETERMINATION OF AVAILABLE IRON IN INDIAN SOILS

An on-line automatic procedure for the flow injection analysis (FIA) d etermination of iron (Fe) in a variety of soil extracts with common la boratory reagents, i.e., thiocyanate, thiocyanate +1, 10-phenanthrolin e/bipyridine has been tested. The apparent molar absorptivity of the c omplexes lies in the range of (5.5-7.0) x 10(3) L mole(-1) cm(-1) at a n absorption maximum between 470-495 nm. The detection limit of the me thod is 15 ppb Fe. The sample output is 100 samples/hr. Almost all ion s associated with Fe in the soil extract do not interfere in this meth od. Optimization of FIA variables, composition of the complex, and eff ect of other ions on the determination of Fe are discussed. The method has been used for determination of Fe status in a variety of agricult ural soils in east Madhya Pradesh, India.