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Byline: H. D. Revanasiddappa (1), T. N. Kiran Kumar (1) Abstract: A new, simple, highly sensitive spectrophotometric method for the determination of trace amounts of cerium(IV) is described. The method is based on the oxidation of leuco disulphine blue (LDSB) to its blue form of disulphine blue by Ce(IV) in a sulfuric acid medium (pH 1.3--3.0) the absorbance of the formed dye is measured in an acetate buffer medium (pH 3.0--4.8) at 635 nm. The color system obeys Beer's law in the concentration range from 0.5 to 5.5 ug mL.sup.--1 cerium with a molar absorptivity of 1.75 x 10.sup.4 L mol.sup.--1 cm.sup.--1 and a Sandell's sensitivity of 0.008 ug cm.sup.--2. All variables were studied in order to optimize the reaction conditions. The developed method has been successfully applied to the determination of cerium in high purity rare-earth oxides, soil, natural water, plant tissue, human hair, and rock samples. Author Affiliation: (1) Department of Chemistry, University of Mysore, Manasagangothri, Mysore, 570 006, India Article History: Registration Date: 11/10/2004

Byline: H. D. Revanasiddappa (1), T. N. Kiran Kumar (1) Abstract: A sensitive and selective spectrophotometric method for the determination of trace amounts of chromium(VI) is described, based on diazotization and coupling reactions. Chromium(VI) oxidizes hydroxylamine in acetate buffer of pH 4.0 +- 0.5 to nitrite, which then diazotizes p-aminoacetophenone to form diazonium salt. The diazonium salt is then coupled with a new coupling agent, citrazinic acid in an alkaline medium, which gives an azo dye with an absorption maximum at 470 nm, a molar absorptivity of 2.12 x [10.sup.4]L [mol.sup.--1]cm.sup.--1, and a Sandell's sensitivity of 0.00246 ug/cm.sup.2. The color is stable for 6 h and the system obeys Beer's law in the range 2--15 ug chromium(VI) in a final volume of 10 mL. The detection limit of chromium(VI) is 0.04 ug/mL. Chromium(III) can be determined after it is oxidized with bromine water in an alkaline medium to chromium(VI). The developed method has been successfully applied to the analysis of chromium in alloy steels, industrial effluents, and pharmaceutical preparations. Author Affiliation: (1) Department of Chemistry, University of Mysore, Manasagangothri, Mysore, 570 006, India Article History: Registration Date: 08/10/2004