Simultaneous determination of copper, lead and cadmium in tantalum by square-wave polarography

Copper, lead and cadmium at the ppb level in high-purity tantalum metal are determined simultaneously by square-wave polarography after removal of tantalum by anion exchange. A 1-g sample is dissolved in a mixture of hydrofluoric and nitric acids in a Teflon beaker, and the solution (20 ml, 4 M in F- and 0.5 M in NO3-) is introduced onto an anion-exchange column (Bio·Rad AG 1-X8, 100200 mesh, 10 mmφ × 150 mm, polyethylene tubing). Then 20 ml of the mixed acid (4 M HF +0.5 M HNO3) is passed through the column. The effluent is evaporated to dryness and the residue is dissolved in 5 ml of the supporting electrolyte containing 0.5 M potassium chloride-0.1 M hydrochloric acid. The lower limits of determination are 0.05 ppm for copper, 0.1 ppm for lead, and 0.02 ppm for cadmium, and the precision is about 10% at the 0.2 ppm level. The time required for a determination is approximately 5 to 6 hours.