Determination of free state manganese(II) in a decoction of a traditional Chinese medicine based on a kinetic spectrophotometric method

Abstract

The chemical state of trace elements in decoctions of traditional Chinese medicines is a new research subject in the chemical studies of traditional Chinese medicine. A simple and sensitive kinetic spectrophotometric method is proposed for the determination of free manganese(II). The method is based on the catalytic effect of manganese(II) on the oxidation of Malachite Green by potassium periodate. The reaction was followed spectrophotometrically by measuring the rate of change in the absorbance of the coloured Malachite Green at 615 nm. Trace amounts of manganese(II)(0.2–2 ng) can be determined with good accuracy and reproducibility; the detection limit is about 0.1 ng. Only iron(III) and aluminium(III) interfere in the determination but these can be masked by fluoride. This method has been used to analyse decoctions of traditional Chinese medicines for trace amounts of free manganese(II) without separation.