バナジウム(IV)は,塩素酸イオンによるヨウ化物イオンのヨウ素への,酸性溶液中での酸化反応を触媒する.その反応速度式を積分すると,log[I<SUP>-</SUP>]は時間<I>t</I>とともに直線的に変化するので,電位変化速度を知ることにより,触媒バナジウム(IV)の定量が可能である.検量線を作成するにあたって,ヨウ化カリウム,硫酸および塩素酸カリウムの最適濃度の決定には, 実験計画法を適用した.本法によれば,0.55〜2.8μ<I>M</I> のバナジウム(IV)の定量が可能であり,比色法とほぼ同じ感度を示した.また,妨害イオンについても検討を行なった. The oxidation of iodide ion to iodine by chlorate ion takes place in an acidic environment according to<BR>ClO<SUB>3</SUB><SUP>-</SUP>+6I<SUP>-</SUP>+6H<SUP>+</SUP>=Cl<SUP>-</SUP>+3I<SUB>2</SUB>+3H<SUB>2</SUB>O<BR>and is catalysed by V(IV). The reaction rate is determined by measuring the iodide ion concentration, which can easily be determined by the potential of iodide-selective electrode. Integration of the kinetic eqn. yields log[I<SUP>-</SUP>]=-<I>K</I>·<I>C</I><SUB>k</SUB>[ClO<SUB>3</SUB><SUP>-</SUP>][H<SUP>+</SUP>]2<I>t</I>+log[I<SUP>-</SUP>]<BR>where <I>K</I> is the rate constant, <I>C</I><SUB>k</SUB> the concentration of V(IV), <I>t</I> time, and [I<SUP>-</SUP>] the initial concentration. The potential change of the iodide-selective electrode is recorded, from which the time required for the potential change of 40 mV is estimated at the linear part of potential-time curve. The rate is proportional to the concentration of catalyst and so it is possible to determine a small amount of V(IV).<BR>The most suitable concentrations of KI, H<SUB>2</SUB>SO<SUB>4</SUB> and KClO<SUB>3</SUB> were decided by the method of experimental design of three-sided classification. The variance ratio concerning the concentration of KI, as well as KClO<SUB>3</SUB>, is very high, <I>i.e</I>. the rate of reaction depends significantly on these concentrations. It is not found, however, that there is a strong interaction between the KI, the H<SUB>2</SUB>SO<SUB>4</SUB> and the KClO<SUB>3</SUB> concentration. The most suitable concentrations of KI, H<SUB>2</SUB>SO<SUB>4</SUB> and KClO<SUB>3</SUB> are 2 μ<I>M</I>, 1 m<I>M</I> and 0.3 <I>M</I>, respectively. A calibration curve with a good linearity was obtained and by this method it is possible to determine V(IV) in the concentration range from 0.55 to 2.8 μ mol dm<SUP>-3</SUP> in the reaction solution. This sensitivity is almost the same as that of spectrophotometric method developed by Yatsimirskii. Fe(III) shows a strong interference.
ヨウ化物イオン電極によるバナジウム(IV)の接触分析
分析化学23(10)_1157-1160.pdf
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