Spectrophotometric determination of copper with iodide ion and Crystal Violet

硫酸酸性溶液中でCu(2+)に対して過剰のI(-)が存在すると,I(-)は酸化されて三ヨウ化物イオン(I(-)(3))となり,Cu(2+)はジヨード銅(I)酸イオン(CuI(-)(2))となる.生成したI(-)(3),CuI(-)(2)はクリスタルバイオレット(CV(+))の存在下でイオン会合体となり,トルエンに抽出される.このトルエン相の607nmにおける吸光度を測定すれば,銅を定量することができる.検量線より算出した見掛けのモル吸光係数は1.7×10(5)1 mol(-1)cm(-1)であった.Fc(III),Cr(III),Co(II)などの酸化性及び還元性物質の共存は定量を妨害するが,その他多くのイオンは多量共存しても妨害とはならない.更に抽出化学種について検討した結果,主な抽出種はI(-)(3)とCV(+)の1:1のイオン会合体であり,大部分の銅イオンは水相に残っていることを確認した.これらのことから,本抽出系では銅(II)イオンは触媒的作用をしているものと結論された.A method for spectrophotometric determination of micro amounts of copper with iodide ion and Crystal Violet (CV) was developed. The method is based on the formation of triiodide ion by the oxidative reaction of iodide ion with copper(II) in dilute sulfuric acid solution and the extraction of triiodide ion into toluene as an ion association complex with CV. The main extracted species is expected to be an ion association complex, CV(+)I(-)(3) copper(II) acts as a catalyst. The recommended procedure is as follows. Take a sample solution containing copper(II) up to 1.6 μg into a 25-ml stoppered test tube. Add 1 ml of 0.46 M sodium iodide solution, 1 ml of 0.5 M sulfuric acid solution and 1 ml of 3.2×10(-4)M CV solution, and dilute the solution to 10 ml with distilled water. Shake the mixture with 5 ml of toluene for 8 min. After the phase separation, measure the absorbance of the organic phase at 607 nm against the reagent blank. The calibration graph shows linearity up to 2.5×10(-6) M of copper(II) in the aqueous phase, and the apparent molar absorptivity is 1.7×10(5)1 mol(-1) cm(-1). Small amounts of oxidizing and reducing agents such as Fe(III), Cr(III) and Co(II) interfered with the determination. The present method is very simple and has a high sensitivity