Determination of manganese in some medicinal plants and their infusions by a kinetic spectrophotometric method

The catalytic effect of manganese (II) on the oxidation of the azo dye Acid Black 1 with potassium periodate in the presence of 1,10-phenanthroline in weakly acidic media is investigated. The reaction is followed spectrophotometrically by measuring the decrease in the absorbance of the azo dye at 618 nm. Under the optimum conditions (3 x 10(-5) mol/L azo dye, 6 x 10(-4) mol/L potassium periodate, 1 x 10(-4) moI/L 1,10-phenanthroline, 0.1 mol/L buffer - pH 4.0, 60degreesC, 5 min) manganese (II) in the range 0.08-4 ng/mL can be determined by the fixed-time method with the detection limit of 0.025 ng/mL. The method developed is highly sensitive, selective and simple. It has been applied successfully to analyse infusions of some medicinal plants (dandelion, common marigold, cowslip and common yarrow) for trace amounts of free manganese (II) without separation and total manganese. Total manganese was also determined in these plants.