フローテーション/対イオン交換抽出法による極微量リン酸及びヒ酸の吸光光度定量

フローテーション/対イオン交換抽出法を用いる極微量リン酸,及びヒ酸の吸光光度定量法を確立した.オルトリン酸とモリブデン酸との反応により生成したモリブドリン酸にマラカイトグリーン(MG(+))をイオン会合させ,この会合体を水相と有機相(シクロヘキサン+イソブチルメチルケトン=8+1v/v)の界面にフローテーションさせる.この後,MG(+)と近い極大吸収波長をもつ染料陰イオン(A(-)と略記)とモリブドリン酸を交換し,(MG(+)・A(-))イオン会合体を有機相(フローテーション溶媒+1,2-ジクロロエタン)に抽出する.ヒ酸も類似のイオン会合体を形成するため,同様にして定量することができる.A-としては新規合成酸性染料の4'-ヒドロキシ-3,5,3',5',2",6"-ヘキサクロロフクソン(以後,Cl(6)BZと略記)を用いた.リンを基準とした見掛けのモル吸光係数は620nmで5.7×10(5)dm(3)mol(-1)cm(-1)であった.この方法によるRSDは1×10(-6)Mのリン酸で0.29%(n=10)であった.本法は試薬から試験値が0.005と低く,6倍の濃縮も可能であり,これによりsub-ppb(10(-10)gml(-1))レベルのリンの定量が可能となった.又ヨウ化物イオン,過塩素酸イオン,ラウリル硫酸イオンなどのイオン会合抽出されやすい疎水性イオンの影響は,溶媒抽出法に比べはるかに小さいことが分かった.本法を海水,鉄鋼試料中のリン,ヒ素の定量に応用した.

Flotation-pairing ion exchange-extraction and spectrophotometric determination of trace amounts of phosphate and arsenate were examined. Ion association complexes of heteropoly acids and a bulky cationic dye floated on the interface between an aqueous and a less polor organic solvent phase. After the flotation, the heteropoly acids were exchanged for an anionic dye, which have a high molar absorptivity and the similar maximum absorption wavelength to the cationic dye. The sum of the absorbances of the cationic and the anionic dyes was measured. In this work, malachite green (MG(+)) and 4'-hydroxy-3,5,3',5',2",6"-hexachlorofuchsone (Cl(6)BZ), a hexachloro derivative of benzaurin, were used as a cationic and an anionic dye. The recommended procedure for phosphate determination is as follows. To a 50-cm(3) separatory funnel, take sample solution (up to 10 cm(3)); if arsenate coexists, add 0.1 cm3 of 2×10(-2) M Na(2)S(2)O(3) to reduce arsenate to arsenite. Then, add 1 cm(3) of 10 M hydrochloric acid, 1 cm(3) of 0.4 M (as Mo) molybdate, 0.5 cm(3) of 5×10(-4) M Malachite Green, and 2 cm(3) of flotation solvent (Isobutyl methyl ketone + cyclohexane= 1 +8 v/v). After shaking for 5 min, discard the aqueous phase, and wash the organic phase 2 times with 5 cm(3) of water. After 1 cm(3) of 2×10(-4) M anionic dye solution, 8 cm(3) of 1, 2-dichloroethane and 5 cm(3) of borax buffer (pH 9) are added, shake 10 times by hands. After the phase separation, measure the absorbance of the organic phase at 620 nm. As arsenate reacts under the same conditions as phosphate, arsenate can be determined by subtracting the amounts of phosphate from the total amounts of phosphate and arsenate which were obtained in the absence of Na(2)S(2)O(3). The apparent molar absorptivity of phosphate or arsenate was 5.7×10(5) dm(3) mol(-1) cm(-1), and the absorbance of the reagent blank was 0.005. Six times concentration was achieved when 30 cm(3) of aqueous phase and 5 cm(3) of extraction solvent were used. Bulky anionic ions, such as iodide, perchlorate and lauryl sulfate, did not interfere with the determination of phosphate and arsenate. This method was applied to the determination of phosphate in seawater and iron and steel samples.