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Determination of anionic surfactants in real samples using a low-cost and high sensitive solid contact surfactant sensor with MWCNTs as the ion-to-electron transducer

MWCNT was used as a conducting substrate at construction of an all solid contact anionic surfactant sensor which used 1, 3-didecyl- 2methylimidazolium-tetraphenylborate (DMI-TPB) ion pair as the sensing element implemented in PVC membrane. SEM and EIS were used for morphological and electrochemical characterization of the sensor. The investigated sensor showed a Nernstian response for DS (57, 1 mV/decade of activity between 2, 0 x 10-7 - 1, 1 x 10-3 M) and a sub-Nernstian response for DBS (51, 1 mV/decade of activity between 3, 6 x 10-7 - 6, 6 x 10-4 M). It responded in 7 seconds for each ten-fold concentration change in the range of 1 x 10-6 M - 5 x 10-4 M. The detection limits for DS and DBS in water were 1, 2 x 10-7 and 2, 6 x 10-7 M, respectively. The sensor revealed a stable potentiometric response in a pH range between 3 and 13 with a signal drift of 1, 9 mV/hour, and exhibited outstanding selectivity performances for DS toward the majority of organic and inorganic anions most frequently employed in commercial formulations based on surfactants. The new sensor was applied for the end-point location at potentiometric anionic surfactant titrations. CTAB was used as a standard cationic titrant by all titrations. The EONSs with higher content of EO groups in the molecule, and the higher concentrations of EONS reduce the magnitude of inflexion of titration curves and may cause their remarkable distortion at AS determination. The sensor was tested at determination of ASs in commercial detergent products and the results were compared with those obtained with the standard two-phase titration method exhibiting the satisfactory mutual agreement. The developed low-cost surfactant sensor had an operational life-time amounted ca 4 months.

anionic surfactant sensor ; MWCNT ; potentiometric titration ; commercial products ; EIS ; SEM

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