Abstract
Catalytic analysis of trace manganese using Stilbazo has been investigated in the presence of ethylenediamine and hydrogen peroxide. Stilbazo was decomposed by the hydroxy radical formed with hydrogen peroxide in the presence of trace Mn(II). The reaction rate was enhanced by ethylenediamine, which acts as an activator in addition to a masking agent. The concentration of Mn(II) was estimated by measuring the decrease in the absorbance of Stilbazo(S). The absorbances of Stilbazo were measured at the start and then t minutes after the reaction-start, respectively. The relation between [S]t and [Mn2+] is ln[S]t= -k [Mn2+]t, +ln[S]0. Here, [S]0 and [S]t denote the concentrations of Stilbazo at the initial state and, then t minutes after reaction-start. In the above, k is the apparent reaction rate constant. This reaction was considered to be pseudo-first order regarding S. A calibration curve showed linearity over the range 01.2 ppb at t=5. The detection limit of Mn(II) by the proposed method was 10 ppt. This method was applied to tap-water samples. The results showed good agreement with the values obtained from flameless atomic-absorption spectrophotometry. Diverse ions (Ca(II), Co(II), Cr(III), Cu(II), Ni(II), Ti(IV) and V(V)) did not interfere with the determination of Mn(II) at 0.8 ppb. On the other hand, Fe(III), Zn(II) and Al(III) interfered with the determination of Mn(II) in the presence of more than 50-fold the Mn(II) concentration.
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