An investigation into the suitability of bismuth as an alternative to gold-amalgam as a working electrode for the in situ determination of chemical redox species in the natural environment

The suitability of the bismuth film working electrode was investigated as an alternative to the gold-amalgam electrode used in solid state microelectrodes for in situ voltammetric analysis of redox chemistry in the natural environment (e.g., lakes, oceans, sedimentary pore waters). Chemical redox species measurable with the Au-amalgam include O-2, H2S, S-x(2-), S2O32-, Fe2+, Fe3+, Mn2+, I-. Bismuth was electrochemically deposited to form a solid film analogous to the Au-amalgam on a polished gold disk electrode. The useable potential window of the Bi-film was found to be narrower than that of the Au-amalgam, precluding the detection of dissolved O-2, I- and S2O32-, whose redox potentials fall outside the Bi-film's range. The Bi-film was able to detect free H2S/HS- and total sulfide (AVS), but not Fe2+ or Mn2+. The Bi-film was less sensitive to low levels of total sulfide (< 10 mu M) than the Au-amalgam; however, the Bi-film was able to accurately quantify very high concentrations of sulfide (at least 15 mM), with a linear response up to an order of magnitude higher than that of the Au-amalgam. Thus the Bi-film appears to have limited application as an alternative to the Au-amalgam microelectrode for in situ analysis of redox species in natural waters.