Hydrogen sulfide coulometric titration

The oxidation of sulfite and thiosulfate becomes facile in the presence of iodide and novel disposable microband sensor electrodes have been developed by Williams and coworkers [187] to allow fast amperometric determination. A similar approach was proposed for the determination of sulfite in wine [188]. In this method, a coulometric titration is carried out in which S(IV) is indirectly oxidized to S(VI). Speciation of SO2 and sulfite was achieved down to micromolar levels. Sulfide and hydrogen sulfide can be determined elec-trochemically in the presence of an iodide mediator [189]. This process may be further enhanced at elevated temperatures. 

Oxidative microcoulometry has become a widely accepted technique for the determination of low concentrations of sulfur in petroleum and petroleum products (ASTM D-3120). The method involves combustion of the sample in an oxygen-rich atmosphere followed by microcoulometric generation of tri-iodide ion to consume the resultant sulfur dioxide. This distinguishes the technique from reductive microcoulometry, which converts sulfur in the sample to hydrogen sulfide that is titrated with coulometrically generated silver ion. 

---