Kinetic Determination of Tantalum in the Presence of Niobium

Abstract

The rates of the ligand substitution reactions of niobium and tantalum complexes involving oxalate, tartrate, citrate or nitrilotriacetate as an auxiliary complexing agent with 4-(2-pyridylazo) resorcinol have been studied spectrophotometrically in acidic media. In the citrate system at pH 5, the maximum difference in rate of substitution between the niobium and the tantalum complexes was achieved. Under the chosen conditions, where the total concentrations of citrate and 4-(2-pyridylazo)resorcinol are 2×10⁻² and 1×10⁻⁴ mol dm⁻³ respectively, the absorbance change during the reaction progress can be kinetically separated for each metal ion and less reactive tantalum in the range 10⁻⁶–10⁻⁵ mol dm⁻³ can be determined by a logarithmic extrapolation method. In the determination of 5×10⁻⁶ mol dm⁻³ of tantalum, the presence of 5-fold amounts (by molarity) of niobium can be tolerated. The effects of 52 diverse ions were examined.