SPECTROPHOTOMETRIC DETERMINATION OF FE(III) IN ALKALINE-SOLUTIONS WITHOUT NEUTRALIZATION

Spectrometric study on the complexation of Fe(III) with an organic rea gent obtained by coupling 3-methyl-1-phenyl-5-pyrazolone with diazotiz ed 3-hydroxy-4-amino-benzene sulphonic acid was carried out in alkalin e solutions. A 1:2 Fe(III): reagent water soluble complex is formed. T he optimum pH is 9.0-11.8. The maximum absorbance of the complex lies at lambda = 560 nm, where the absorbance of the reagent is low. The mo lar absorptivity is 9000 l.mole-1.cm-1 at pH = 11.6. The value of the stability constant determined at 20 +/- 1-degrees-C, pH = 11.6 and lam bda = 560 nm is 4 x 10(5)M. The Beer-Lambert law is followed for iron concentration in the 0.2-5.0 mug/ml range. The spectrophotometric meth od was tested on synthetic solutions and thus applied for determinatio n of traces of Fe(III) in several samples of alkaline hydroxides and c arbonates without the neutralization of the solutions.