Automatic determination of ionic surfactants in an aqueous medium by a photometric titration method

A fully automatic photometric titration method was developed for the determination of anionic and cationic surfactants in a one-phase aqueous system with tetrabromophenolphthalein ethyl ester (TBPE) used as an indicator. To avoid decomposition of the TBPE indicator in the presence of an anionic surfactant in acidic solutions, the buffer and indicator solutions were automatically added to sample solutions just before titration. In an indirect titration method for cationic surfactants, cationic surfactants were automatically determined under the same conditions as in the titration of anionic surfactants. The usual samples were analyzed for less than 10 min at concentrations of 10(-6)10(-3) mol dm(-3). The relative standard deviations of the determination of various surfactants were 0.20.3%. The proposed method was applied to many practical samples. The results, except for those for anionic surfactants possessing polyoxyethylenyl groups and several cationic surfactants, were in good agreement with the results obtained by the JIS titration method (Epton method).微分光度滴定法を用いて,水溶液でのイオン性界面活性剤の自動分析システムの構築について検討した.滴定終点決定の指示薬であるテトラブロモフェノールフタレインエチルエステル(TBPE)は界面活性剤との共存系では経時的に分解するため滴定直前に自動添加すること,及び陽イオン界面活性剤は逆滴定法の採用により自動化システムを構築し,同一条件下で陰イオン及び陽イオン界面活性剤の自動連続定量(10分/件)が可能となった.本滴定法で10(-6)～10(-3)Mの濃度範囲の陰イオン及び陽イオン界面活性剤が定量でき,再現性は0.2～0.3%と良好であった.各種実際試料について応用した結果,陰イオン界面活性剤において,一部の親水性の高い活性剤(オキシエチレン基を特に多数含む活性剤)以外はJIS法(Epton法)と非常に良い一致を示し,又陽イオン界面活性剤においても,JIS法とほぼ一致した