Abstract
A simple, rapid and highly sensitive method has been developed for the determination of trace manganese and applied to determination of trace manganese in tap water. The method is based on the catalytic action of Mn(II) in the oxidation of catechol {or 2, 3-dihydroxynaphthalene(DHN)} by hydrogen peroxide, which is coupled with the reaction between the formed o-benzoquinone and ethylenediamine. By using catechol, a linear relationship between the concentration of Mn(II) and the observed absorbance at 380 nm (reference: water) was obtained over the range of 0.0533.8 ppb, under the optimum conditions, i.e., pH 10.0, buffered by ethylenediamine-HCl, 5.4 × 10-3 M (=mol dm-3)catechol, 3.0% hydrogen peroxide, 1.2 M ethylenediamine; temperature, 30°C and reaction time of 5 min. By using DHN, Mn(II) can be determined in the range of 0.0908.0 ppb {pH 10.0, 3.6× 10-3 M DHN, 1.2% hydrogen peroxide; 1.8 M ethylenediamine; temperature, 30°C; reaction time, 10 min and abs. at 434 nm (reference: water)}. Iron(II) and (III) have showed positive interference at more than 100 times the amount of Mn(II) (2.0 ppb) because they make stable red complexes with catechol or 2, 3-dihydroxynaphthalene. The results of determinations of trace Mn(II) in tap water showed good agreement with the values obtained by flameless atomic absorption spectrophotometry.
