A selective polypyrrole-based sub-ppm impedimetric sensor for the detection of dissolved hydrogen sulfide and ammonia in a mixture

An impedance-transducer sensor was developed for in situ detection of hydrogen sulfide (H2S) and ammonia (NH3) in aqueous media. Using cyclic voltammetry (CV), polypyrrole (PPy) was deposited on the surface of the microfabricated interdigitated gold electrode. Due to the proton acid doping effect of H2S on PPy and ionic conduction of the film, the sensor showed a decreasing impedance response to H2S unlike other reducing chemicals, i.e., ammonia (NH3). The recorded faradaic data was then associated with an equivalent circuit and compared with that of NH3 to examine the selectivity of the sensor. An electrochemical impedance spectroscopy (EIS) analysis was applied to the mixture of H2S and NH3 prepared at different ratios for the concentrations ranging from 2 ppm to 20 ppm (below 2-ppm, no response was observed due to the formation of NH4HS, not sensible with PPy). The principal component analysis (PCA) was used to train a real-time prediction model for both classification (for the type of the analyte) and regression (the concentration of the analyte). The results showed the high performance of the sensor in determining individual analytes while the model was able to accurately predict the amount of H2S and NH3 in the mixture.