DETERMINATION OF TANTALUM WITH HEXAFLUOROTANTALATE(V)-SELECTIVE COATED GRAPHITE ELECTRODE

A hexafluorotantalate(V)-selective coated-graphite electrode was prepa red by coating a graphite rod with brilliant green-hexafluorotantalate (V) extract in 1-chloronaphthalene in a PVC matrix. Potential measurem ents were made against an HF-resistant plastic sleeve (Ag/AgCl) extern al reference electrode. The concentrations of sulfuric and hydrofluori c acids, for the optimum response of the electrode to hexafluorotantal ate(V), were found to be 1 M each in the test solutions. The electrode responded to hexafluorotantalate(V) in the linear range 5.0 x 10(-6) - 5.0 x 10(-3) M, with a slope of -58 mV per decade and detection limi t of 8.0 x 10(-7) M within 5 - 15 s. The relative standard deviation f or six determinations of 1.0 x 10(-4) M tantalum(V) was 2%. The life-t ime of the electrode was 60 days. The effects of forty diverse ions on the electrode response to the hexafluorotantalate(V) were studied and the electrode was found to be highly selective to hexafluorotantalate (V). Niobium, the element that commonly occurs with tantalum ores, sho wed a very low level of interference. The newly developed coated-graph ite electrode has been applied to the determination of tantalum in tan talite-columbite ores and several synthetic matrices by direct, sample addition, standard addition, and Gran's plot potentiometric technique s with reasonable precision (2-4%) and accuracy.