ABSTRACT
Cyanide-containing waste or water on contact with sulfides can form thiocyanates. On chlorination, the thiocyanate could react with chlorine to form highly toxic cyanogen chloride, CNCl. Thiocyanate in water may be analyzed using colorimetric method and spot test. Thiocyanate reacts with ferric ion under acidic conditions to form ferric thiocyanate, which has an intense red color. The intensity of color of the ferric thiocyanate formed is proportional to the concentration of thiocyanate ion in the sample. Thiocyanate reacts with chloramine-T on heating at pH below 8 to form cyanogen chloride, CNCl. The latter forms red color after adding pyridine–barbituric acid reagent. This test is similar to that of cyanide. Therefore, prior to chloramine treatment, the sample is treated with formaldehyde to mask the effect of cyanide. Reagents are added after pretreatment of the sample. The spot test is performed in a porcelain spot plate with 6–12 cavities. The test is performed using a few drops of sample, standards, and reagents.
