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Abstract

Spectrophotometric methods were employed to study the chelate formation between Fe(III) ions and 2-(5-bromo-2-pyridylazo)-5-(diethylamino)phenol (BrPADAP) in dimethylformamide (φ = 20%) and Triton X-100 (φ = 0·1%). The ML₂ chelate with absorption maxima at 535 and 590 nm and molar absorption coefficients of 6·5 and 8·2 m² mmol^-1 is formed quantitatively in the pH interval 3·5 - 4·0 for at least a seven-fold concentration excess of BrPADAP. Concentrations of c(Fe) = 1·6 - 8·1 μmol l^-1 can be determined independently in 0·1M acetate buffer with pH 3·6. Iron and copper ions can be determined simultaneously in the presence of zinc ions in binary or ternary mixtures in the concentration ranges c(Fe) = 2 - 8 μmol l^-1 and c(Cu) = c(Zn) = 3 - 16 μmol l^-1. The relative deviations in the calculated concentrations, Δc_r, are 1 - 4% for Fe and up to 5% for Cu in binary and ternary mixtures with equivalent concentrations up to a concentration excess of one component of five-fold in binary mixtures or of one or two components of up to three-fold in ternary mixtures. The simultaneous determination of Zn(II) is accompanied by a Δc_r value of up to 30 - 50% and cannot be recommended under the given experimental conditions.