4,6-ジ-t-ブチル-3-メトキシカテコールとマラカイトグリーンを用いるモリブデン(VI)の抽出/吸光光度定量

Mo(VI)の高感度抽出/吸光光度定量法について検討を行った.pH1.8から3.5の範囲でMo(VI)と4,6-ジ-t-ブチル-3-メトキシカテコール(DBMC)は1価のキレート陰イオンを形成し,マラカイトグリーンとのイオン会合体としてトルエンに抽出される.吸収極大波長635nmでの見掛けのモル吸光係数は8.0×10(4) 1 mol(-1)cm(-1)であり,試薬から試験の吸光度は約0.01であった.又,Mo(VI)1.92μgでの10回繰り返し実験の相対標準偏差は0.52%であった.通常の金属イオンは定量を妨害しないが,W(VI)及びV(V)は2×10(-7)Mが共存許容濃度である.V(V)はアスコルビン酸を加えることにより2.5×10(-5)Mまで共存できる.W(VI)は酒石酸添加により10(-6)Mまでマスキングできたが,これ以上の濃度の場合には補正式を用いた.本法を鉄鋼試料中のMo(VI)の定量に応用し,満足な結果が得られた.

Mo(VI) forms an chelate anion with 4, 6-di-t-butyl-3-methoxycatechol (DBMC) and the ion asscoiate between the chelate anion and Malachite Green (MG) is extracted into toluene in the pH range from 1.8 to 3.5. DBMC was synthesized according to our previous work. The standard procedure was as follows: transfer a sample solution {Mo (VI) <4.8 μg} into a 25 ml test tube with stopper, and add 0.5 ml each of 5×10(-2) M sulfuric acid and 1.0×10(-3) M MG solution. If necessary, add masking agent solution (ascorbic acid and tartaric acid). After adding water to make up to 10 ml, add 5 ml of 1.5×10(-2) M DBMC toluene solution, then shake for 30 min. Measure the absorbance of the organic phase at 635 nm.Apparent molar absorptivity was 8.0×10(4) l mol(-1) cm(-1) and the absorbance of the reagent blank was 0.01. The relative standard deviation of 10 measurements of 1.92μg of Mo(VI) was 0.52%. The present method was applied to steel samples with satisfactory results. The effect of W(VI) coexisting at concentrations over 1×10(-6) M was corrected by the equations using apparent molar absorptivities of Mo(VI) and W(VI) obtained with or without the masking agent (2.5×10(-3) M tartaric acid).