DETERMINATION OF FREE STATE MANGANESE (II) IN DECOCTIONS OF SOME MEDICINAL PLANTS BY A KINETIC SPECTROPHOTOMETRIC METHOD

The catalytic effect of manganese (II) on the oxidation of the azo compound 2ʹ,4ʹ -Dihydroxyazo-benzen-4-sulphonic acid sodium salt, with potassium periodate in the presence of 1,10phenanthroline 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. Johnʹs wort, smoke-tree, and silver lime blossom) for trace amounts of free manganese (II) without separation and total manganese.