This method is used to determine the apparent hydrogen sulfide concentration in amine solution. Two procedures, a Control and a Precision method are included. Hydrogen sulfide is determined by oxidation with standard iodine solution in an acidic medium. The term apparent is used here as iodine is reactive to other species, such as organic sulfide and inorganic sulfite anions. However with respect to amine solution from tail gas recovery, thiosulfate ion is more relevant.
Thiosulfate, if present, is also oxidized and is included as apparent H2S in the calculation. Thiosulfate may be determined by using UOP Method 818, and the value thus obtained subtracted from the apparent H2S concentration. The lower limit of detection is approximately 25 grains/gallon or 0.04 g/L.