Carbethoxypentadecyltrimethylammonium bromide

Other detection methods are based on optical transmittance [228-231], Alcohol sulfates have been determined by spectrophotometric titration with barium chloride in aqueous acetone at pH 3 and an indicator [232] or by titration with Septonex (carbethoxypentadecyltrimethylammonium bromide) and neutral red as indicator at pH 8.2-8.4 and 540 nm [233]. In a modified two-phase back-titration method, the anionic surfactant solution is treated with hyamine solution, methylene blue, and chloroform and then titrated with standard sodium dodecyl sulfate. The chloroform passing through a porous PTFE membrane is circulated through a spectrometer and the surfactant is analyzed by determining the absorbance at 655 nm [234]. The use of a stirred titration vessel combined with spectrophotometric measurement has also been suggested [235]. Alternative endpoint detections are based on physical methods, such as stalag-mometry [236] and nonfaradaic potentiometry [237]. 

An alternative approach is to use hydrophobic indicators, which remain in the chloroform layer throughout the titration and give a very sharp colour change. Eppert and Liebscher [15] used dimethyl yellow (cationic) in titrations with carbethoxypentadecyltrimethylammonium bromide (Septonex). The colour change in the chloroform layer is from pink to yellow and is very sharp. Tsubouchi and Matsuoka [16] used the potassium salt of the ethyl ester of tetrabromophenolphthalein (anionic) for titration with tetradecyldimethylbenzylammonium chloride (Zephir-an) in a solution buffered at pH 6. The chloroform layer starts off yellow, becomes green near the end-point and turns sky blue when one drop of excess titrant is added. 

Markd-Monostory, B., S. Borzsonyi, Oil-soluble sulphonic acids and sulphonates by two-phase titration with carbethoxypentadecyltrimethylammonium bromide (Septonex), Tenside, 1985,22,265-268. 

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See also in sourсe #XX -- [ ]

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