HEXAFLUOROTANTALATE(V)-SELECTIVE COATED GRAPHITE ELECTRODE BASED ON MALACHITE GREEN

An attempt was made to develop hexafluorotantalate(V)-selective coated graphite electrodes based on Malachite Green, Crystal Violet, and Eth yl Violet using 1-chloronaphthalene, tri-n-butyl phosphate, and dimeth yl phthalate as plasticizers. The electrode prepared by coating Malach ite Green-hexafluorotantalate(V) extract in 1-chloronaphthalene with a PVC matrix on a graphite rod was found to give a Nernstian response t o hexafluorotantalate(V) in a wide concentration range. Potential meas urements with the coated graphite electrode were made against a plasti c sleeve HF-resistant Ag/AgCl external reference electrode. Optimum re sponse 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 x 10(-5) - 1.0 x 10(-2) mol/L tantalum(V), 58.0 +/- 1.5 mV/deca de, and 3.98 x 10(-6) mol/L tantalum(V), respectively. The relative st andard deviation for six determinations of 5 x 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-ta ntalate(V) were studied, and the potentiometric selectivity coefficien ts were evaluated. The electrode was found to be highly selective to h exafluorotantalate(V) and free from interference of niobium which comm only 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 techniqu es and the results were in good agreement with the actual or certified values.