Microsensor for total dissolved sulfide (TDS)

Total Dissolved Sulfide (TDS) concentrations can either be derived from simultaneous measurement of pH and one of the sulfide species or determined indirectly in samples following an acidification step. Here we report a microsensor that allows for direct measurement of TDS in aquatic media without the need for pH monitoring. An acidic chamber placed in front of a commercial, amperometric H₂S microsensor allows for the in-situ conversion of dissolved ionic sulfide species to H₂S, which in turn is oxidized at the transducer anode. A typical sensor had a tip opening of 30 μm, a response time of <50 s and linear range between 0.5 and 650 μM. The sensor performance can be largely tuned by altering the geometry of the chamber. Sensors of different sensitivity (0.04-2.93 pA/μM) showed no noticeable change in zero current and sensitivity during continuous polarization over 7 weeks. The sensor was successfully applied to resolve microscale TDS gradients in freshwater and marine sediments. Other avenues of application include the online monitoring of industrial and urban sewers.