Abstract
The suitability of m-aminophenols as a catalytic indicator for the determination of manganese(II) with EDTA was evaluated. Manganese(II) catalyzes the oxidation of aromatic amine and phenol derivatives by hydrogen peroxide in hydrogen-carbonate ion solutions. The effect of substituent groups on the catalytic oxidation of the indicator was investigated. and the criteria for the selection of the indication reaction were briefly discussed. The optimum catalytic action of manganese(II) ion was limited in carbonate concentrations of (0.30.4) M and pH ranges between 8.4 and 9.7. In N, N-dialkyl-m-aminophenol indicator system, the absorption maximum of the oxidation products shifts to longer wavelength and bathochromic effect of substituent group was observed. The recommended procedure for manganese determination is; add 3 ml of 0.2% m-aminophenol(I) {or N, N-diethyl-m-aminophenol (II)} and 1 ml of 3% hydrogen peroxide to about 50 ml portion of 0.4 M carbonate solution containing known amounts of EDTA. Titrate the solution with a manganese(II) solution. At the end point, the solution turns deep orange(I) or violet(II) by the catalytic action of manganese(II). This catalytic titration method was applied to the determination of zinc, cadmium, mercury and lead by back-titration of excess of EDTA with standard manganese(II) solution. The results were in good agreement with those obtained by the standard titrimetric method with metal indicators. The coefficient of variation for the catalytic titration of manganese was 0.1 %.
