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ABSTRACT
An attempt was made to develop hexafluorotantalate(V)-selective coated graphite electrodes based on Malachite Green, Crystal Violet, and Ethyl Violet using 1-chloronaphthalene, tri-n-butyl phosphate, and dimethyl phthalate as plasticizers. The electrode prepared by coating Malachite Green-hexafluorotantalate(V) extract in 1-chloronaphthalene with a PVC matrix on a graphite rod was found to give a Nernstian response to hexafluorotantalate(V) in a wide concentration range. Potential measurements with the coated graphite electrode were made against a plastic sleeve HF-resistant Ag/AgCl external reference electrode. Optimum response of the electrode was observed in test solutions made 1 mol/L in both sulphuric and hydrofluoric acids. The concentration range, slope, and detection limit from the plot of E vs log [Ta(V)] were found to be 1.0 × 10−5 – 1.0 × 10−2 mol/L tantalum(V), 58.0 ± 1.5 mV/decade, and 3.98 × 10−6 mol/L tantalum(V), respectively. The relative standard deviation for six determinations of 5 × 10−4 mol/L tantalum(V) was estimated to be 2%. The response time of the electrode was found to be 5-15 s and the electrode functioned properly for three months. The effects of diverse ions on the electrode response to hexafluoro-tantalate(V) were studied, and the potentiometric selectivity coefficients were evaluated. The electrode was found to be highly selective to hexafluorotantalate(V) and free from interference of niobium which commonly occurs with tantalum. The analytical application of the electrode was extended to the determination of tantalum in tantalite-columbite ores and several synthetic matrices using four potentiometric techniques and the results were in good agreement with the actual or certified values.