Abstract
For the determination of microamounts of chromium in pure iron, as the spectrophotometric method by using diphenylcarbazide lacks in sensitivity, the organic solvent extraction method was studied as follows.
One tenth gram of sample is dissolved in hydrochloric acid and nitric acid, and the iron is removed by extraction with the mixture of two parts of methyl-iso-butylketone and one part of amyl acetate. The lower layer is evaporated to almost dryness after nitric acid is added.
It is dissolved with 10 ml of sulfuric acid (1.4 v/v %), 1 ml of potassium permanganate solution (0.1 % ) is added and boiled for 3 minutes. After cooling, 10 ml of urea solution (20%) is added and sodium nitrite solution (10%) is added dropwise until the pink color is extinguished. The solution is put in a separating funnel, diluted to 25 ml with water, 3 ml of diphenyl carbazide (0.2%) alcohol solution is added and stood for one minute.
Eight ml of sulfuric acid (1+1), 5 g of anhydrous sodium sulfate and 10.0 ml of iso-amylalcohol are added to the solution and shaken vigorously for one minute. After the upper layer is separated, the absorbancy at 543 mμ is measured againstiso-amylalcohol as a blank. Ten folds of Al, As, B, Ca, Ce, Co, Cu, Mg, Mn, Mo, Nb, Ni, P, Pb, Sn, Ta, Ti, V, W, and Zn do not interfere. From 0.1 to 50 ppm of chromium was determined within about one hour.
