水溶液内イオン会合反応に基づくイオン性界面活性剤の定量

The determination of ionic surfactants was carried out on the basis of ion association between ionic dyes and ionic surfactants in an aqueous medium. Three kinds of dyes (tetrabromophenolphthalein ethyl ester(TBPE), methyl orange analogues and nitrophenylazophenol analogues) were used as novel ion-association reagents. The ion-association constants between cationic surfactants (Q(+)) with dyes (D(-)) and anionic surfactants (A(-)) were obtained. It was found that the hydrophobic interaction plays an important role in the formation of stable ion associates. On the basis of the ion association accompanying a color change, the analytical methods for the determination of ionic surfactants, such as a batchwise spectrophotometric method, a flow-injection method and a photometric titration method, were developed in the presence of a small amount of nonionic surfactant in an aqueous medium. In particular, the photometric titration method was examined in detail. Titration curves could be simulated by using the ion-association constants of both ionic surfactants and indicators with a titrant, quaternary ammonium ion. By using the simulation method of the titration curves, an evaluation of the end-points and selection of the desirable titration conditions were possible. The ionic surfactants at concentrations of the 1 × 10(-6) M level can be determined by the photometric titration method. The proposed titration method was applied to several practical samples; the results were in good agreement with both the results of the JIS titration method (Epton method) and a solvent-extraction method with ethyl violet.

水溶液でのイオン性界面活性剤の定量について研究した.発色反応試薬系としては,酸性染料のテトラブロモフェノールフタレインエチルエステル(TBPE),陰イオン性アゾ染料のメチルオレンジ系及びフェニルアゾフェノール系試薬について検討した.これらの試薬陰イオンを用いて陽イオン界面活性剤とのイオン会合定数及び陽,陰イオン界面活性剤間のイオン会合定数を求め,反応性について考察した.これらのイオン会合反応に基づき,バッチ法による吸光光度定量,フローインジェクション吸光光度定量,光度滴定について検討した.特に新しい試みとして,イオン会合滴定法について詳細な検討を行った.イオン会合滴定における滴定曲線を,試料イオンと滴定イオン間のイオン会合定数,指示薬とのイオン会合定数を用いてシミュレーションし,微分による滴定終点と当量点との整合性について考察した.本滴定法では,10(-6)Mまでの陽イオン界面活性剤及び陰イオン界面活性剤が定量できる.又,実際試料の滴定結果は二相滴定法のJIS法及び溶媒抽出吸光光度法とよく一致した.