Photometric determination of hafnium in iron and steel, using Arsenazo III in nitric acid solution

A method for the photometric determination of 0.010.5% hafnium in iron and steel with Arsenazo III in nitric acid solution has been newly studied. The absorbance in the nitric acid solution is more independent on the acid concentration than in the hydrochloric acid solution. The molecular extinction coefficient is 1.4×105. The established procedure is as follows. Two tenth g. sample is decomposed with nitric acid, hydrofluoric acid and perchloric acid, and evaporated to white fumes. One tenth aliquot is taken and 65 ml of nitric acid and 5 ml of 10% urea solution are added. The solution is diluted with water to 100 ml, after 10 ml of 0.1% Arsenazo III solution is added. Hafnium is determined from the absorbance at 665 mμ. The determination was carried out in the presence of iron within an absolute error of 0.005%. The time required for an analysis was about 30 min. Elements commonly present in iron and steel except zirconium scarcely interfered.