Determination of trace amount of chromium by square-wave polarography

Abstract

The substitution reaction of chromium(III) with Cd-EDTA has been investigated, and it was found that the reaction could be used for the determination of chromium.
At the pH range from 3 to 4, the reaction proceeded quantitatively by heating the solution for more than 45 minutes in boiling water. On the other hand, the wave height of free cadmium ion dissociated from Cd-EDTA decreased as the pH value of the solution increased, but the change of the wave height was negligible at the pH value above 4. Hence, it was desired that the substitution reaction was done at pH 3 to 4 and the measurement of the amount of substituted cadmium was done at pH above 4.
Linear relationship was found between the concentration of chromium and the peak current of cadmium, over the concentration range from 5×10^-6 to 3×10^-5 M of chromium.
Many metal ions except alkaline earth elements, manganese and cobalt interfered, but the interference from molybdenum could be eliminated by adding small amount of mannitol, and that from iron and aluminum. could be removed by applying the acetylacetonechloroform extraction.