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Study of the interaction of nonionic and cationic surfactants using a nanomaterials based surfactant sensor

Nonionic surfactants (NS) are used in a wide range of products for cosmetic, industrial, agricultural and household applications. In combination with ionic (cationic or anionic) surfactants they improve some functional performances of commercial products, but also have ecotoxic properties, therefore their determination is of great importance. The most commonly used class of NS are ethoxylated nonionic surfactants (EONS) that are frequently used in mixtures with cationic surfactants (CSs) to develop product formulations that combine the properties of both CSs and EONSs. Therefore, the influence of chemical nature and concentration of EONSs on the potentiometric titration of CSs was investigated. A new potentiometric sensor, sensitive to cationic surfactants was prepared, containing MWCNTs modified with a sulfate group and cetylpyridinium ion (CP) embedded in 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 titration curves of cetylpyridinium chloride (CPC) alone and those with the addition of EONS containing different number of ethoxy (EO) groups were comapred. The standard solution of sodium dodecyl sulfate (NaDS, c = 4 mM) was used as the titrant. EONSs affected the titration curves, moderately reducing their extent and inflection. The number of EO groups did not significantly influence the titration curve or the reliable quantification of CSs. The influence of the EONS concentration on the potentiometric titration of CSs was investigated too. It can be concluded that an increase of EONS concentration resulted in a slight decrese of inflection at the equivalence point, but not influencing CSs determination.

Nonionic surfactants ; cationic surfactants ; MWCNT ; potentiometric sensor

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