Electrochemical detection of trace hydrogen sulfide in gaseous samples by porous silver electrodes supported on ion-exchange membranes (solid polymer electrolytes)

A highly sensitive and fast-responding electroanalytical sensor for the determination of hydrogen sulfide in gaseous atmospheres is described which eliminates oxygen interferences. It consists of a porous silver working electrode (facing the sample) supported on one face of an ion-exchange membrane, which serves as a solid polymer electrolyte. The other side of the membrane faces an internal electrolyte solution containing the counter and reference electrodes. The performance of this sensor has been tested for the electroanalysis of H2S by amperometric monitoring, cathodic stripping measurements, and now injection analysis. In all cases, the device displays a high current sensitivity and a low background noise, so that quite low detection limits (45 ppb v/v, 0.07 ppb v/v, and 3.7 x 10(-13) mol in amperometric, cathodic stripping, and flow injection measurements, respectively) are estimated for a signal-to-noise ratio of 3. The responses are found to be characterized by both a good reproducibility and a linear dependence on the concentration of H2S over fairly wide ranges, as well as by a short response time (ca. 0.5 s to attain a 95% response). 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 any effect due to the most important potential interfering species and the possibility of adopting such a device for the direct detection of H2S in ambient air and for industrial hygiene measurements are discussed.