Potentiometric titration with sodium tetraphenylborate

The indicator electrode is a platinum sheet electrode. The reference electrode may be silver-silver chloride or a calomel electrode filled with 2 M sodium chloride instead of potassium chloride. 

Condition the indicator electrode by doing a blank titration, but ignore the result. 

Weigh into a 150 ml beaker a sample containing about 0.5 millimol of active. Dissolve in 15.00 ml glacial acetic acid containing benzethonium chloride, heating if necessary. 

Dilute to about 100 ml with boiling water. Insert the electrodes and titrate potentiometrically, with continuous stirring, with 0.05 M NaTPB to just beyond the point of inflection. 

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A number of authors have described the potentiometric titration with sodium tetraphenylborate (TPB), NaB(C6H5)4, of the pseudocationic... 

FIG. 1 Potentiometric titration with sodium tetraphenylborate of a mixture of a cationic (cetylpy-ridinium chloride) and an amphoteric (cocoamidopropylbetaine) surfactant, followed with a specially made PVC-membrane electrode. The first inflection is due to titration of the cationic and the second to titration of the amphoteric surfactant. (Reprinted with permission from Ref. 81. Copyright 1992 by Karl Hanser Verlag.)... 

A sensitive potentiometric surfactant sensor was prepared based on the highly lipophilic l,3-didecyl-2-methyl-imidazolium cation in the form of its tetraphe-nylborate associate. The sensor responded fast and showed a Nemstian response for the following surfactants under investigation CPC, CTAB, and hyamine with slope values of 59.8, 58.6, and 56.8 mV decade respectively. The sensor served as an end-point detector in ion-pair surfactant potentiometric titrations using sodium tetraphenylborate as titrant. Several technical grade cationic surfactants and a few commercial disinfectant products were also titrated, and the results were compared with those obtained from a two-phase standard titration method. The results, compared to those obtained using a commercial surfactant electrode with the standard two-phase titration method, exhibited satisfactory mutual agreement. 

Some specialty cationics which are not sufficiently hydrophobic for direct potentiometric titration with tetraphenylborate can be determined indirectly. An excess of sodium tetraphenylborate is added to precipitate the surfactant, which is removed by filtration. Excess tetraphenylborate ion in the filtrate is then determined by titration with thallium(I) nitrate (110). This last procedure was used for determination of the amount of a cationic surfactant fixed to cotton fibers in a textile dying bath. 

A commercially available fluoroborate ion-selective indicator electrode was used for the potentiometric titration of surfactants and soaps.The titrants were HDTAC, hexadecylpyridinium chloride (HDPC), and diisobutylphenoxy-ethoxyethyI-(dimethyI)benzyIammonium chloride (DIPEBC). Similarly, Benoit et al. " titrated CTAB with sodium tetraphenylborate potentiometrically using a commercial CI04 selective electrode. The method proved to be precise exhibiting a relative standard deviation of 1.1 %. 

Vytfas K, Dvofakova V, Zeman I (1989) Titrations of non-ionic surfactants with sodium tetraphenylborate using simple potentiometric sensors. Analyst 114 1435-1441... 

A mixture consisting of 25 mL of an aqueous (0.2 to 1.0 mM) solution of chlorpromazine hydrochloride and 5 mL of 0.1 M acetate buffer (pH 3.3) was titrated to a potentiometric endpoint with 0.0 IM sodium tetraphenyl-borate [77]. The titrant was added at a rate of 0.36 mL/min with continuous stirring, and the temperature of the medium was maintained at 22 2°C. The end point was detected by a tetraphenylborate-selective electrode. 

Shoukry et al. have prepared plastic membrane ion-selective electrodes for the determination of procaine and other anaesthetic compounds [69]. The electrode selective for procaine was prepared with the use of a membrane containing 15% of the procaine tetraphenylborate ion pair with 40% of dioctyl phthalate and 45% of poly vinyl chloride (PVC). The membrane was attached as a disc (12 mm diameter, 0.3 mm thick) to the polished PVC cap of the electrode tube, which contained an internal solution of 0.1 M sodium chloride made 1 mM in the same drug, and in contact with a Ag-AgCl wire. Linear response ranges were determined to be 20.0 pM to 16 mM for procaine over the pH range of 3.1 to 7.9. The electrodes could also be used in the potentiometric titration of the drug with 0.01 M sodium tetraphenylborate. 

A sample containing 5-50 mg ethoxylate in about 90 mL water is mixed with 10 mL of 0.1 M barium chloride solution and titrated with 0.01 M aqueous sodium tetraphenylborate solution (prepared with 10 g polyvinyl alcohol and 10 mL 0.1 M NaOH per liter of titrant). The titration is made potentiometrically, using the Metrohm surfactant indicating electrode and a silver/silver chloride reference electrode (NaCl filling solution). The electrode must be rinsed free of precipitate after every few titrations using methanol. An electrode... 

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