The determination of tervalent chromium and iron in chromic acid.
Chromic acid is analysed for tervalent chromium by separation of Cr(III) from Cr(VI) by precipitation as the hydrous oxide, with Zn(OH)(2) as a carrier. The hydrous oxide is collected by centrifugation and dissolved in perchloric acid, then Cr(III) is complexed with 1,2-diaminocyclohexanetetra-acetic acid and measured spectrophotometrically at 540 mmicro. Repetitive analysis of a sample of chromic acid showed 93 ppm of Cr(III) (s = 13, n = 9). Iron in chromic acid is also separated as the hydrous oxide, then dissolved in HCl, reduced to Fe(II) with hydroxylamine hydrochloride, complexed with bathophenanthroline disulphonic acid and measured spectrophotometrically at 533 mmicro. Repetitive analyses of a sample of chromic acid showed 2-6 ppm of iron (s = 0.35, n = 8).
Fuhrman
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PPG Industries, Chemical Division, P.O. Box 4026, Corpus Christi, Texas, U.S.A.
Latimer
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