Fig. 1. Diagram of the polarographic sulfide sensor, PSS. A side view and expanded tip view of the PSS illustrates the component parts. The overall dimensions are 25 mm long and 12 mm diameter, with individual components proportionally sized. The sawtooth lines indicate threaded pieces. The platinum anode and cathode are cemented into the polyether ether ketone (PEEK) housing with epoxy resin. The membranes are cemented together with silicone cement. The 0.5 mm hole in the H₂S-impermeable membrane is concentric with the anode and provides a small reservoir of electrolyte between the anode and the H₂S permeable membrane. Lateral diffusion of H₂S from this region at the tip into the bulk electrolyte is limited and greatly shortens response time as the impermeable membrane serves as a virtual guard ring.