A new solid-state anionic surfactant-selective sensor based on functionalized MWCNT.

A new solid-state potentiometric sensor for anionic surfactants (AnS) determination was prepared. The sensor material in the liquid membrane was made of multi-walled carbon nanotubes (MWCNTs) chemically functionalized with a quaternary ammonium group and tetraphenylborate (TPB) anion (MWCNT-N(CH)TPB). The response of the MWCNT-N(CH)TPB sensor was Nernstian (59.3 mV/decade of activity) for both AnS investigated (sodium dodecyl sulfate (NaDDS) and sodium dodecylbenzenesulfonate (NaDBS)). The limits of detection were 2.0 ∙ 10 and 1.5 ∙ 10 for NaDDS and NaDBS, respectively, and the average response time was only 5 s. The new MWCNT-N(CH)TPB sensor was very selective for NaDDS compared to anions usually contained in commercial products and is not affected by nonionic surfactants that can also be present in these products. It was tested to determine AnS concertation by the potentiometric titration method in a pH range between 3 and 12 and successfully applied for its determination in three-component mixtures and real systems.