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Abstract
The catalytic effect of manganese (II) on the oxidation of the azo compound 2′,4′ -Dihydroxy-azo-benzen-4-sulphonic acid sodium salt, with potassium periodate in the presence of 1,10- phenanthroline in weakly acidic media is studied. The reaction is followed spectrophotometrically by measuringthe decrease in the absorbance of the azo compound at 490 nm. Under the optimum conditions (7×10−5mol dm−3 azo compound, 4×10−4mol dm−3 potassium periodate, 1×10−4mol dm−31,10-phenanthroline, 0.1 moldm−3 buffer –pH 4.5, 70°C, 8 min) manganese (II) in the range 0.1–5ng cm−3 can be determined by the fixed-time method with the detection limit of 0.03 ng cm −3. The developed method is highly sensitive, selective, and simple. The method was applied successfully to analyse decoctions of some medicinal plants (common centaury, common St. John's wort, smoke-tree, and silver lime blossom) for trace amounts of free manganese (II) without separation and total manganese.