A New Sensor for Determination of Anionic Surfactants in Detergent Products with Carbon Nanotubes as Solid Contact
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A new solid-state sensor for potentiometric determination of surfactants with a layer of multi-walled carbon nanotubes was prepared. As a sensing material, 1,3-didecyl-2-methylimidazolium–tetraphenylborate ion-pair was used. The investigated sensor showed a Nernstian response for both dodecylbenzenesulphonate (DBS, 57.6 mV/decade of activity between 5 × 10−7 to 1 × 10−3 M) and sodium lauryl sulfate (LS, 58.4 mV/decade of activity between 2 × 10−7 to 2 × 10−3 M). It responded in 8–10 s for each ten-fold concentration change in the range of 1 × 10−6 to 3 × 10−3 M. The detection limits for DS and DBS were 2 × 10−7 and 3 × 10−7 M, respectively. The sensor revealed a stable response (signal drift 2.6 mV/h) and exhibited satisfactory selectivity performances for LS over most of the anions generally used in surfactant-based commercial detergents. The main application of this sensor was the end-point determination in potentiometric titrations of anionic surfactants. The (diisobutyl phenoxy ethoxy ethyl)dimethyl benzyl ammonium chloride (Hyamine), cetyltrimethylammonium bromide, hexadecylpyridinium chloride monohydrate (HDPC) and 1,3-didecyl-2-methylimidazolium chloride were tested as potential cationic titrants, and all exhibited analytically usable titration curves with well-defined equivalence points. The standard solution of HDPC was used as a cationic titrant by all potentiometric titrations. The operational life-time of the sensor described was prolonged to more than 3 months.
KeywordsSurfactant sensor MWCNT Anionic surfactant Potentiometric titration Detergents
This work has been supported by the Croatian Science Foundation under the project IP-11-2013.
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