Comparison of sulfide-selective electrode and gas-stripping monitors for hydrogen sulfide in effluents

A commercial prototype monitor, in which a sulfide-selective electrode detects hydrogen sulfide with a pH electrode used as the reference electrode in a sample acidified to pH <5, is compared to a monitor in which a solid-state sensor detects hydrogen sulfide stripped from the sample by an air—CO₂ mixture. Each monitor has a detection limit of ?0.005 mg kg^-1 and both monitors performed well over a six-month period in the field, sampling a heavy water plant effluent. Both monitors are simple to operate, calibrate, and maintain, but their accuracies are affected by oil and particulates in the sample. Advantages of using the suifide/glass electrode detection system in acidic solutions are presented.