A new high-sensitivity potentiometric sensor for anionic surfactants was fabricated using the dimethyldioctadecylammonium-tetraphenylborate (DDA-TPB) ion associate as an ionophore that was incorporated into a liquid PVC membrane. Carbon powder was used for immobilization of the ionophore in the membrane, thus significantly reducing its ohmic resistance and reducing its signal drift. The sensor exhibits a sub-Nernstian response for both dodecylbenzenesulfonate (DBS) and dodecyl sulfate (DS) in H2O (55.3 and 58.5mV/decade of activity, respectively) in a range between 3.2×10-7 and 4.6×10-3M for DS and 2.5×10-7 and 1.2×10-3M for DBS. The sensor also exhibited a sub-Nernstian response for DS and DBS in 10mM Na2SO4 (55.4 and 57.7mV/decade of activity, respectively) between 2.5×10-7 and 4.6×10-3M for DS and 1.5×10-7 and 8.8×10-4M for DBS. The detection limits for DS and DBS in H2O were 2.5×10-7 and 2.0×10-7 M and in 10mM Na2SO4 the detection limits were 2.5×10-7 and 1.2×10-7 M, respectively. The response time of the sensor was less than 5s for changes at higher concentration levels (above 1×10-4M) in both water and 10mM Na2SO4. At lower concentrations (below 1×10-5M) the response times were 8 and 6s in water and 10mM Na2SO4, respectively. The signal drift of the sensor was 1.2mV/hour. The new carbon-based sensor exhibited excellent selectivity performance for DS over almost all of the anions commonly present in commercial formulations and it was successfully employed as an end-point detector in potentiometric titrations of anionic surfactants in a pH range from 3 to 12. Three-component mixtures containing sodium alkanesulfonate (C10, C12 and C14) were successfully differentially titrated.
Keywords: Anionic surfactant sensor; Carbon powder; Effluents; Industrial products; Potentiometric titration.
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