Removal of sulfide odor is accomplished by aeration or chlorination. Hydrogen sulfide is a toxic substance that acts as a respiratory depressant in both humans and fish. The range is dependent on the pathlength used. The range listed above is based on a pathlength of 1.8 cm. Under suitable conditions the sulfide ion reacts with p-aminodimethylaniline and ferric chloride to produce methylene blue in proportion to the sulfide concentration.
Ammonium phosphate is added to remove the color due to the ferric iron.
Samples that are used for total sulfide concentrations may be preserved by adding 2M zinc acetate solution at the rate of 2 mL per liter of sample. This precipitates sulfide as inert zinc sulfide. Determination of dissolved sulfides and sample not preserved with zinc acetate must be started within 3 minutes of sampling. Interferences Strong reducing agents such as sulfite, thiosulfate, and hydrosulfite prevent the formation of the color or diminish its intensity. High concentrations of sulfide will inhibit the reaction, but dilution of the sample prior to analysis eliminates this problem.