Spectrophotometric determination of the average valence of cerium in Nd-Ce-Cu oxides with ο-tolidine
1998 Volume 47 Issue 3 Pages 171-177
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1998 Volume 47 Issue 3 Pages 171-177
The spectrophotometric determination of the average valence of Ce in Nd-Ce-Cu oxides was performed using ο-tolidine. Each sample was dissolved in a HCl solution in the presence of ο-tolidine, which was oxidized with Ce(IV) in a 2e step to intensely yellow quinonediimine in a weakly acidic solution. Then, Ce(IV) was reduced to Ce(III). Ce(IV) was determined over the range of 0.320μg based on the absorbance observed at 437 nm on the oxidant of ο-tolidine. The optimum conditions for the determination of Ce(IV) in Ce oxides were as follows: total volume, 6ml; ο-tolidine concentration, 1.7×10-3%; pH, 1.0 (adjusted with HCl); reaction time, 2min; reaction temperature, 65°C; sample amount taken, 0.21.1 mg. On the other hand, the total Ce was determined by inductively coupled plasma atomic-emission spectrometry. The average valence of Ce (nav) could be calculated according to the following equation: nav ={[Ce (IV)]/ [Ce]total}+3. The average valence of Pr in the Pr-Ba-Cu-O semiconductor was determined by the same procedure as that proposed for Ce. Cu(III) did not interfere with the determination of Ce(IV) and Pr(IV). The average valence of Ce in a sample was obtained to be 3.23. The results agree well with those obtained by the KMnO4 method. By the proposed method, the lower limit of Ce(IV) determination was 0.3 μg and the amount of consumed sample could be decreased down to 0.2 mg.
