Colorimetric analysis by the mercury (II) thiocyanate method. Thiocyanate ion is liberated from mercuric thiocyanate through sequestration of mercury by analyte chloride ions (this forms un-ionized but soluble mercuric chloride). The liberated thiocyanate ion then forms reddish yellow ferric thiocyanate in the presence of excess ferric ions from ferric nitrate. The yellow ferric thiocyanate is measured colorimetrically on a Lachat 8500 FIA at 480nm. Alternatively, chloride can be determined by ion-chromatography on a Dionex 120 ion chromatograph.
(See Method References No. 43 and No. 51)