Determination of cationic surfactants in pharmaceutical disinfectants using a new sensitive potentiometric sensor.

A new sensitive potentiometric surfactant sensor was prepared based on a highly lipophilic 1,3-didecyl-2-methyl-imidazolium cation and a tetraphenylborate antagonist ion. This sensor was used as a sensing material and incorporated into the plasticized PVC-membrane. The sensor responded fast and showed a Nernstian response for investigated surfactant cations: cetylpyridinium chloride (CPC), hexadecyltrimethylammonium bromide (CTAB) and Hyamine with slope 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 sensor showed satisfactory analytical performances within a pH range of 2-11, and exhibited excellent selectivity performance for CPC compared to all of the organic and inorganic cations investigated. The influence of the nonionic surfactants on the shape of titration curves was negligible if the mass ratio of ethoxylated nonionic surfactants and cationic surfactants (EONS:CS) was not greater than 5.