AbstractHydrogen is often formed in sulfidic environments where interference from hydrogen sulfide has prevented its analysis by amperometric hydrogen microsensors. Hydrogen microsensors were made insensitive to hydrogen sulfide by placing a sulfide trap (guard) containing solutions of heavy metal ions, sulfide-oxidizing ferricyanide, or alkaline chemicals at the sensor tip. The overall most efficient sulfide guard consisted of a solution of ZnCl2 in propylene carbonate which resulted in absence of interference from 5mmolL−1 hydrogen sulfide and also alleviated any interference from oxygen. The hydrogen sensors with ZnCl2-propylene carbonate traps could be used at temperatures up to 60°C without exhibiting excessive baseline currents. The ability of a guarded sensor to resolve the hydrogen distribution in a sulfidic microbial mat with up to 2.4μmolL−1 H2 was demonstrated.