Cetylpyridinium chloride, titration

EXPERIMENTAL PROCEDURES AUTOMATED TURBIDIMETRIC TITRATION. A method for the automated aqueous turbidimetric titration of surfactants has been published (10) in which anionic surfactants are titrated against N-cetylpyridinium chloride to form a colloidal precipitate near the equivalence point. N-cetylpyridinium halides have a disadvantage in that they have the tendency to crystallise out of solution (15), consequently the strength of the solution may alter slightly without the knowledge of the operator, also the crystals suspended in solution may cause damage to the autotitrator. In view of these drawbacks hyamine was preferred as the titrant. 

Potassium poly (vinyl alcohol) sulfate (PVSK) was standardized against 2.5 X 10" N cetylpyridinium chloride monohydrate. A 1-mL ahquot of a 200-600-ppm copolymer solution was combined with 1 drop of toluidine blue indicator and agitated with a magnetic stirrer. PVSK was added dropwise until the endpoint was reached. Each titration was repeated a minimum of four times. 

Dissolve an amount of powdered tablets equivalent to about one-quarter of a tablet in a mixture of equal volumes of acetate buffer solution, pH 3 7 (see p. 116) and water and dilute to 200 ml with the mixture in a graduated flask. Transfer a 10-ml aliquot of this solution to a dry beaker, add, with swirling, 15 ml of 0 01 M sodium tetraphenylboron, allow to stand for five minutes and filter through a dry, sintered-glass crucible. Pipette 20 ml of the filtrate into a flask, add 0 50 ml of bromo-phenol blue indicator and titrate the excess sodium tetraphenylboron with 0 005M cetylpyridinium chloride to the blue end-point. Repeat the operation omitting the sample. 1 ml O OIM sodium tetraphenylboron = 0 0003910 g potassium. 

Two-phase titration is usually less sensitive to interference from other foreign (nonsurfactant) species. When applied to anionic surfactant systems, two-phase titration is primarily used for the analysis of alkyl sulfates and sulfonates. Typical titrants in these applications are solutions of cetylpyridinium bromide, cetyltrimethylammonium bromide, and benzyldimethylalkyl (C12 or C14) ammonium chloride. The most accurate results are, however, obtained with p-tert-octyl-phenoxy-ethoxy-ethyl-dimethyl-benzylammonium chloride, also known under the commercial name of Hyamine 1622. The structure of Hyamine 1622 is shown in Fig. 11-32,a. 

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