A simple, rapid and sensitive spectrophotometric method has been developed for the determination of trace amounts of chromium using variamine blue as a chromogenic reagent. The proposed method is based on the reaction of chromium(VI) with potassium iodide in acid medium to liberate iodine, which oxidizes variamine blue to form a violet colored species having an absorption maximum 556 nm. Beer's law is obeyed in the range 2-12 mug mL-1 of Cr(VI). The molar absorptivity, Sandell's sensitivity, detection limit and quantitation limit of the method were found to be 0.911×10(4) L mol-1 cm-1, 1.14×10-2 mug cm-2, 0.02 mug mL-1 and 0.07 mug mL-1 respectively. The optimum reaction conditions and other analytical conditions were evaluated. The effect of interfering ions on the determination is described. The chromium(III) can be determined after it is oxidized with bromine water in alkaline medium to chromium(VI). The developed method has been successfully applied to the analysis of the chromium in alloy steels, industrial effluents, natural water samples and soil samples.
chromium determination; spectrophotometry; variamine blue
