Photocurable ISFET for anionic surfactants. Monitoring of photodegradation processes

Abstract

The preparation of a new ion-selective field-effect transistor (ISFET) based on a photocurable membrane sensitive to anionic surfactants is described. The membrane is formed by an urethane–acrylate matrix with 2-cyanophenyl octyl ether as the plasticiser. When compared to conventional ion-selective electrodes, the prepared ISFETs do not show significant differences in sensitivity and reproducibility ( P=0.05). When calibrating with dodecylbenzenesulfonate (DBS −) the prepared ISFETs show a nernstian behaviour, with a slope of 57.5 mV per decade. The linear working range is 1.0×10 −3 to 3.0×10 −6 M DBS − and the detection limit is 1.2×10 −6 M. The response times were below 0.7 min in all cases (95% of the step change). As the application, photodegradation processes using titanium dioxide dispersions, were monitored for two common anionic surfactants: DBS −, being aromatic, and the more alkylic dodecylsulfate, DS −. The determination of surfactant concentration was performed following a standard addition methodology, using ISFETs as the sensors, and without any previous separation stages. The degradation kinetics in both cases are first-order processes, with half-life times ( t 0.5) of 31.5 min for DBS − and 52.0 min for DS −.