A SIMPLE SPECTROPHOTOMETRIC DETERMINATION OF TRACE AMOUNTS OF VANADIUM USING THIONIN

A simple and sensitive spectrophotometric method has been developed for the determination of trace amounts of vanadium using thionin as a chromogenic reagent. The proposed method is based on the reaction of vanadium(V) with potassium iodide in acid medium to liberate iodine, which bleaches the violet colour of thionin and is measured at 600 nm. This decrease in absorbance is directly proportional to the vanadium(V) concentration and obeys Beer\'s law in the range of 0.2-10 μgmL-1 of V(V). The molar absorptivity, Sandell\'s sensitivity, detection limit and quantitation limit of the method were found to be 2.298 x 104 Lmol-1cm-1, 0.52 x 10-2 μgcm-2, 0.035 μgmL-1 and 0.11 μgmL-1, respectively. The optimum reaction conditions and other analytical conditions were evaluated. The effect of interfering ions on the determination is described. The developed method has been successfully applied to the analysis of the vanadium in synthetic and alloy samples. KEY WORDS: Vanadium determination, Spectrophotometry, Thionin Bull. Chem. Soc. Ethiop. 2005, 19(2), 155-161