分相滴定法に基づく界面活性剤の自動光度滴定 : III.ジクロロフルオレセインを分相指示薬とするせっけんの定量

長谷川 章, 山中 実

doi:10.2116/bunsekikagaku.33.12_657

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Automatic photometric titration of surface active agents based on two-phase titration; III. Determination of soap using dichlorofluorescein as indicator.
分相滴定法に基づく界面活性剤の自動光度滴定　ＩＩＩ　　ジクロロフルオレセインを分相指示薬とする石けんの定量
ブンソウテキテイホウニモトズクカイメンカッセイザイノジドウコウ
III. Determination of soap using dichlorofluorescein as indicator
III.ジクロロフルオレセインを分相指示薬とするせっけんの定量

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Experimental conditions were studied for the determination of C₆C₁₈ fatty acids by two-phase automatic photometric titration. The salts of fatty acids were back-titrated with standard sodium dodecylsulfate after addition of excess Benzethonium chloride in water-chloroform medium. An automated titrator equipped with porous PTFE (Teflon) membrane separator (previous publications, literatures 1 and 2) was used. Using the method proposed, determination of long-chain fatty acids was satisfactory, while short-chain acids generally gave lower end point (lower recoveries) due to their incomplete extraction. Addition of 14 % 1-propanol into the aqueous solution was effective to improve the recovery of short-chain fatty acids. Among indicators tested (Bromocresol Green and several fluorescein derivatives), 2', 7'-dichlorofluorescein proved to be satisfactory in applicability to wider range of fatty acids and in sharp end-point indicator. Under the recommended conditions, recoveries were 0, 26.3, and 85.4 % for C₆, C₈, C₁₀ acids, respectively;those of the longer-chain fatty acids were quantitative. However, a soap containing a mixture of short-chain fatty acids was successfully analyzed by using the modified molecular weights which were obtained from the experimentally determined recovery of each C₆C₁₀ acid. Typically titration time required was 1520 min per sample, and the relative standard deviation of determination was about 0.3 %.

収録刊行物

分析化学

分析化学 33 (12), 657-662, 1984

公益社団法人日本分析化学会

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