Quantitative determination of a series of alkylcarboxylbetaines by automatic potentiometric titration was studied with emphases as effect of selection of acidification agents, acidification temperature and time on the titralion result with respect to the content of alkylcarboxylbetaines. The results showed that the determination accuracy is significantly affected by the pH of the acidification system as well as the acidification temperature and time. Key issue is to assure the complete acidification of the alkylcarboxylbetaine molecules. By using acetic acid - sodium acetate buffer solution of pH = 3 as acidification system at 70 ～ 80 ℃ for 2 -3 h,the content of C12 - C18 alkyldimethylcarboxylbetaines and bis - dodecylmethylcarboxylbetaine can be potentiometric titrated by sodium dodecyl sulfate (SDS) with satisfactory result and the recovery achieves 97% - 102%. Good results have also be obtained by acidification in sulfuric acid solution of pH = 2 for 1 h at room temperature. For samples of technical grade betaine product, under the titration conditions, content of tertiary amine in the product will participate the titration reaction,so that the titration result is actually the sum of content of alkylbetaine and corresponding tertiary amine. Since the tertiary amine content can be independently measured using suitable method,the content of alkylbetaine can thus be quantitatively identified.%研究了酸化剂种类、酸化温度及时间等对电位滴定法测定烷基摹羧基甜菜碱含量的影响.结果表明,酸化剂的pH,酸化温度和时间等对测定结果有显著影响,关键是保证甜菜碱分子的完全酸化.以pH =3的醋酸-醋酸钠缓冲溶液作酸化体系,于70 ～80℃下酸化2～3h后用十二烷基硫酸钠(SDS)进行电位滴定,对C12-C18单长链烷基甜菜碱以及双十二烷基甜菜碱都能得到满意的结果,回收牢达到97％一102％.以硫酸作酸化剂,将pH提高到2左右,于室温下酸化lh后滴定,亦可得到满意的结果.对工业级甜菜碱样品,其中的游离叔胺在测定条件下也定量参与滴定反应,所得结果为甜菜碱和相应叔胺的总量,由于叔胺含量能用独立的方法测出,借助于电位滴定可以测出甜菜碱含量.
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