Determination of Trace Amounts of Manganese by Flow Injection Spectrophotometry

A new method to detect trace manganese (Ⅱ) at room temperature is developed to avoid the effects of temperature and the durations of heating and cooling. As the catalytic effects of manganese (Ⅱ) can be strongly enhanced by nitrilotriacetic acid (NTA), sodium periodate can oxidize tetrabase \[4,4’ bis(dimethylamino) diphenylmethane\] in an acetate buffer medium (pH=5.2). The unstable blue intermediate product is controlled quickly by flow injection technique and its absorbance is measured at 602nm.A detection limit of 7.3×10 -11 g/mL is achieved at a sampling frequency of 60/h. The linear range of the method is 0～20 μg/L for manganese. The proposed method has been applied to the analyses of several natural waters with satisfactory results.