Potentiometric analysis of ionic surfactants by a new type of ion-selective electrode

A new type of ion-selective electrode for the determination of ionic surfactants is presented. It can be exploited as end-point indicator with a high sensitivity in potentiometric titration of surfactants and for direct potentiometric measurements in an online flow system. The electrode consisted of an ion pair between sodium laurylsulphate and 1,3-didecyl-2-methyl-imidazolium chloride, immobilized in a plasticized PVC membrane. This electrode gives a linear response for sodium lauryl sulphate between 2 × 10−6 and 5 × 10−3 M with, at 22 °C, a slope of 58.9 mV per decade of SLS concentration. The electrode potential fluctuation is less than 1 mV. Application to the analysis of commercial detergent products has been realized and results have been compared with the two-phase titration method.