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Functionalized carbon nanotubes as a new sensing material for cationic surfactant determination

Cationic surfactants (CATs) are used in a wide range of products for cosmetic, industrial, agricultural and household applications, but also they have ecotoxic properties and because of that their determination is of great importance. A new potentiometric sensor, sensitive to CATs was prepared, containing multiwalled carbon nanotubes (MWCNTs) chemically modified with a sulfate group and cetylpyridinium ion (CP) embedded in a plasticized PVC membrane. As a conducting substrate, graphite of spectroscopic grade was employed. The chemical modification of MWCNTs with CP cations significantly improved the most important analytical and practical sensor properties. The new sensor showed a Nernstian response for CP (58.9 and 58.2 mV/decade in water and 0.01 M Na2SO4, respectively) and sub-Nernstian responses for hexadecyltrimethylammonium ion (CTA) (56.6 and 55.5 mV/decade in water and 0.01 M Na2SO4, respectively) and Hyamine (52.1 and 49.7 mV/decade in water and 0.01 M Na2SO4, respectively). The detection limit for CP was 1.2 · 10-7 M (in water and 0.01 M Na2SO4), whereas those for CTA were 2.5 · 10-7 and 3.2 · 10-7 M (in water and 0.01 M Na2SO4, respectively), and that for Hyamine was 1.5 · 10-6 (in water and in 0.01 M Na2SO4). The sensor showed good selectivity for CP cations compared to the inorganic and organic cations commonly present in commercial formulations.

functionalized carbon nanotubes, cationic surfactants, potentiometric titration

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