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Indirect Spectrophotometric Method For The Determination Of Chromium

H.D.Revanasiddappa, B.P.Dayananda

An indirect spectrophotometric method for the determination of chromium is presented. The method is based on the oxidation of hydroxylamine hydrochloride to nitrite by chromium(VI) in an acetate buffer of pH 4.0 ± 0.5 followed by diazotization of the nitrite produced with pnitroaniline under acidic condition and subsequent coupling of the diazonium salt with citrazinic acid in an alkaline medium. The formed azo dye has an absorption maximum at 515 nm. Beer’s law is valid over the concentration range of 0.2 – 1.8 μg ml-1 of chromium(VI). The molar absorptivity and Sandell’s sensitivity of the color system are 2.1 × 104 l mol-1 cm-1 and 2.5 ng cm-2, respectively. The detection limit of chromium(VI) is 50 ng ml-l. Chromium(III) can be determined after it is oxidized with bromine water in an alkaline medium to chromium(VI). The developed method has been applied successfully to determine chromium in alloy steels, environmental and pharmaceutical samples.