Abstract
Determination of small quantity of thallium in cadmium by square wave polarography was studied. One mol hydrochloric acid solution containing hydroxylamine hydrochloride was found to be suitable as the supporting electrolyte, but preliminary separation of tin, cadmium and lead from thallium was necessary.
The recommended procedure is as follows. Five grams of sample is decomposed with aqua regia added with a small amount of water. The solution is evaporated to dryness and evaporated again with hydrochloric acid and saturated bromine water. The residue is dissolved with perchloric acid, evaporated to dryness and made to IM hydrobromic acid solution. Thallium is extracted with ethyl ether, and washed with IM hydrobromic acid in order to remove cadmium. The ether extract is evaporated nearly to dryness. Hydrobromic acid and perchloric acid are added, and evaporated again.
The residue is dissolved with 4.5ml of 6M hydrochloric acid and diluted to 25ml with 5ml of 10% hydroxylamine hydrochloride and water. The oxygen dissolved in the solution is removed by passing nitrogen, and the square-wave polarogram is obtained between -0.25 to -0.75 volt against mercury pool.
As little as 1ppm of thallium in cadmium was determined with good accuracy and reproducibility.
