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 th e determination of hydrogen sulfide in gaseous atmospheres is describe d which eliminates oxygen interferences. It consists of a porous silve r working electrode (facing the sample) supported on one face of an io n-exchange membrane, which serves as a solid polymer electrolyte. The other side of the membrane faces an internal electrolyte solution cont aining the counter and reference electrodes. The performance of this s ensor has been tested for the electroanalysis of H2S by amperometric m onitoring, cathodic stripping measurements, and now injection analysis . In all cases, the device displays a high current sensitivity and a l ow 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 s ignal-to-noise ratio of 3. The responses are found to be characterized by both a good reproducibility and a linear dependence on the concent ration 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 ari ses from the lack of a gas-permeable membrane and direct gas contact t o the triple interphase among the gaseous analyte, the porous working electrode, and the solid polymer electrolyte. The absence of any effec t due to the most important potential interfering species and the poss ibility of adopting such a device for the direct detection of H2S in a mbient air and for industrial hygiene measurements are discussed.