Effect of substituted groups on the analytical sensitivity of tridentate ligand azo-compounds for catalytic analysis of manganese(II)

To improve the analytical sensitivity, the tridentate ligand azo-compounds derivatives of 1-amino-8-hydroxy-7-(o-hydroxyphenylazo)-3, 6-naphthalenedisulfonic acid(7-o-OH)were synthesized, and the effect of substituted groups on the sensitivity was investigated by making a comparison of their color-fading rate.The fading rate of azo-compound increased along with a decrease in the Hammett constant(σ)and an increase in pKa;this was accelerated by substituting electron-donative groups to the compounds.Azo-compounds having electron-donative groups were useful as sensitive reagents for catalytic analysis.The optimum conditions for determining Mn(II)were investigated using the most sensitive reagent, 1-amino-8-hydroxy-7-(o-hydroxy-p-metylphenylazo)-3, 6-naphthalenedisulfonic acid(p-CH3), among the examined azo-compounds.A calibration curve was made between ln(A1/A5)and the concentration of Mn(II)under the optimum conditions:3.0×10-5M p-CH3, 1.5×10-3M, 1, 10-phenanthroline, 1.1×10-1M H2O2, pH10.3, 30°C.The value of ln(A1/A5)was nearly proportional up to 4ppb of Mn(II).The detection limit of Mn(II)was 6ppt.