Simultaneous Determination of Iron and Cobalt by Spectrophotometry with Thivioluric Acid as Chromogenic Reagent

In a borate buffer medium of pH 9.0,stable colored coordination complex was formed between the color reagent,thiovioluric acid (TVA) and iron(Ⅱ) or cobalt(Ⅱ). The coordination complex of TVA and Fe(Ⅱ) showed 2 absorption peaks at wavelengths of 658 nm and 395 nm in its absorption spectrum,while that of TVA and Co(Ⅱ) showed only one absorption peak at 424 nm. It was proposed that determination of iron was performed by measuring the absorbance values at 658 nm,and determination of cobalt at 424 nm where significant absorption of the Fe(Ⅱ)-TVA complex was also happened. Based on the additivity of absorbances of the complexes,a formula for calculation of content of cobalt was given. Linear relationships between values of absorbance and mass concentration of iron and cobalt were found in the ranges within 50.0 μg and 25.0 μg per 25 mL respectively. The proposed method was used for determination of Fe and Co in water samples giving results in consistency with the results found by AAS. Values of recovery found by standard addition method were ranged from 98%-104% and 97%-103% with values of RSD′s (n=5) ranged from 1.8% to 3.4% and 2.2% to 3.7% respectively.