Separation and Recycling for Rare Earth Elements by Homogeneous Liquid-Liquid Extraction (HoLLE) Using a pH-Responsive Fluorine-Based Surfactant
A selective separation and recycling system for metal ions was developed by homogeneous liquid-liquid extraction (HoLLE) using a fluorosurfactant. Sixty-two different elemental ions (e.g., Ag, Al, As, Au, B, Ba, Be, Bi, Ca, Cd, Ce, Co, Cr, Cu, Dy, Er, Eu, Fe, Ga, Gd, Ge, Hf, Hg, Ho, In, Ir, La, Lu, Mg, Mn, Mo, Nb, Nd, Ni, Os, P, Pb, Pd, Pr, Pt, Re, Rh, Ru, Sb, Sc, Se, Si, Sm, Sn, Sr, Ta, Tb, Te, Ti, Tl, Tm, V, W, Y, Yb, Zn, and Zr) were examined. By changing pH from a neutral or alkaline solution (pH ≥ 6.5) to that of an acidic solution (pH 90% efficiency into a sedimented Zonyl FSA® (CF3(CF2)n(CH2)2S(CH2)2COOH, n = 6–8) liquid phase. Moreover, all rare earth elements were obtained with superior extraction and stripping percentages. In the recycling of rare earth elements, the sedimented phase was maintained using a filter along with a mixed solution of THF and 1 M sodium hydroxide aqueous solution. The Zonyl FSA® was filtrated and the rare earth elements were recovered on the filter as a hydroxide. Furthermore, the filtrated Zonyl FSA was reusable by conditioning the subject pH.
Homogeneous liquid-liquid extraction method for the selective spectrofluorimetric determination of trace amounts of tryptophan.
Twenty-one amino acids were derivatized with fluorescamine (FLA) under basic conditions (pH 9) and the extraction of the amino acid-FLA derivatives was investigated using a homogeneous liquid-liquid extraction with perfluorooctanoic acid (HPFOA) based on phase separation under strongly acidic conditions. Under the optimum concentration conditions for the reagents ([PFOA]T = 3 x 10(-3) mol dm-3, [acetone]T = 3 vol.%, [HCl]T = 1.8 mol dm-3), the concentration factor was approximately 1000-fold (i.e., 30 microliters of the sedimented liquid phase was produced from 33 ml of the homogeneous aqueous solution). The percentage extraction (E) was determined for the 21 amino acid-FLA derivatives; the value for the tryptophan (Trp)-FLA derivative was 80.9%, whereas the other derivatives were not almost extracted (E < 0.4%). The Trp-FLA derivative was selective for the extraction using the homogeneous liquid-liquid extraction method with HPFOA. After the sedimented liquid phase containing Trp-FLA has been placed on a polytetrafluoroethylene filter-paper, the fluorescence intensity was determined using a spectrofluorimeter with filter-paper as the solid-sample holder. The calibration graph of Trp was linear over the range 1.0 x 10(-8)-1.5 x 10(-6) mol dm-3. The relative standard deviation for the central value of the calibration graph was 4.5% (five determinations) and the detection limit (S/N = 3) was 8.9 x 10(-9) mol dm-3. When the proposed method was applied to the highly sensitive spectrofluorimetric determination of Trp in animalin-L syrup, the results were satisfactory.
Synthesis of a thermo-sensitive copolymer with hydroxamic acid group and its characteristics of metal-ion collection
均一固相抽出法に用いる金属イオンの捕集媒体として, キレート官能基を有する熱応答性高分子, ポリ(N-イソプロピルアクリルアミド-co-メタクリルヒドロキサム酸) を合成した. そして合成した熱応答性高分子の相転移特性及び金属イオン捕集特性について検討した. 高分子へのヒドロキサム酸基の導入割合が上がるにつれて, コポリマー全体の親水性が増し, 高分子の相転移温度 (下限臨界溶液温度) は上昇し, 凝集相が形成しにくくなった. この高分子は水に均一に溶存し金属イオンと反応することができる. このため, キレート樹脂法による金属イオンの捕集濃縮とは異なり, この高分子を用いることで金属イオンの加水分解反応の影響を受けずに金属イオンを捕集することができた. 特に, 鉄(III) イオンについてはpH5.0～10.0の範囲でほぼ完全に捕集できた. また, コポリマー中のヒドロキサム酸基は金属イオンとは高次錯体を形成していないことが示唆された.