Pulsed amperometric detection of ethanol in breath by gold electrodes supported on ion exchange membranes (solid polymer electrolytes)

A sensitive and fast-responding amperometric sensor for the determination of ethanol in breath which eliminates oxygen interferences is described. It consists of a porous gold working electrode (facing the sample) supported on one face of an ion-exchange membrane which serves as a solid polymer electrolyte (SPE). The other side of the membrane faces an internal electrolyte solution (1 M aqueous NaOH) containing the counter and reference electrodes. The fouling of the gold working electrode, due to the ethanol oxidation process, is overcome by continuously cleaning and reactivating its surface by applying a triple-pulse potential waveform. The performance of this sensor has been tested in a closed-loop flow apparatus fed with synthetic ethanol-vapor samples obtained by evaporating aqueous solutions with known ethanol contents. The sensor displays a high current sensitivity and a low background noise, so that a low detection limit (2 mu g L(-1), 1 ppm v./v.) is estimated for a signal-to-noise ratio of 3. The responses are characterized by both a good reproducibility and a linear dependence on the ethanol concentration over a fairly wide range (more than three orders of magnitude), as well as by a short response time (ca. 1 s). This fast response time arises from the lack of a gas-permeable membrane and direct gas contact to the triple interphase among the gaseous analyte, the porous working electrode and the solid polymer electrolyte. The absence of significant interfering effects and the possibility of adopting such a device for the detection of ethanol in fermentation processes are also discussed.