Conditions for the photometric determination of chromium (VI) with diphenylcarbazide and effect of iron and vanadium

Abstract

Re-examination of conditions for the photometric determination of chromium (VI) with diphenylcarbazide gave the following results: a suitable sulfuric acid concentration, 0.02 to 1.0 N; a suitable volume of 0.25% diphenylcarbazide solution, 0.5 to 2.0 ml per 25 ml of final solution. The acetone solution of diphenylcarbazide was more stable than the ethanol solution. Five diphenylcarbazide reagents commercially available were tested. They could be divided into two groups-one giving a molar absorptivity of 4.3 × 10⁴l mol^-1 cm^-1 at 542 nm and the other giving 3.5 × 10⁴. The result of the elemental analysis indicated that the latter group reagents were an approximately equimolar mixture of diphenylcarbazide and phenylsemicarbazide. In the determination of 1 to 10μg of chromium in 0.2 or 0.5 N sulfuric acid solution, 0.1 mg of iron (III) did not interfere if an Eastman diphenylcarbazide was used. However, an appreciable error was observed if a Tokyo Kasei Kogyo reagent was used. When either of the reagents was used, 0.1 mg of vanadium (V) did not interfere with the determination of 1 to 10 μg of chromium in 0.2 or 0.5 N sulfuric acid solution.