Development of a new ion-selective field-effect transistor sensor for anionic surfactants: Application to potentiometric titrations

The application of optimised poly(vinyl chloride) matrix, anionic surfactant-sensitive membranes to ion-selective field-effect transistors (ISFETs) is described. The developed devices showed a lifetime longer than four months, improving reported values of PVC membrane-ISFETs. Other characteristics are Nernstian slopes from 59 to 62 mV/dec, detection limits of about 10-6 M and good linearity. They also showed response to several anionic surfactant species and to the reagent used for the potentiometric titration. This allowed the measurement of the overall anionic surfactant content in different samples. Apart from the basic characteristics of the membranes, this report also shows the results of potentiometric titrations using the developed ISFETs with known samples. The devices were useful in a range from 0.02 to 10 mM for dodecylbenzenesulphonate solutions. End-point potential jumps up to 250 mV were obtained in the titrations. The reproducibility, expressed as relative standard deviation, was estimated, using a standard 4 mM sodium dodecylsulphate solution, as 1.45% (n = 14). Finally, in a comparative study, there were no significant differences between the results produced with the standard, two-phase titration method and the proposed potentiometric titration method using surfactant ISFETs as end-point indicators.