This method quantifies the amount of Cl in a water sample. Thiocyanate ion is liberated from mercuric thiocyanate by the formation of soluble mercuric chloride. In the presence of ferric ion, free thiocyanate ion forms the highly colored ferric thiocyanate, of which the absorbance is proportional to the chloride concentration. The absorbance of the ferric thiocyanate is read at 480 nm. The method has a detection limit of 0.1 meq L-1 Cl and is generally reproducible within 5%.
Diamond, D. 1994. Determination of Chloride by Flow Injection Analysis Colorimetry. QuikChem Method 10-117-07-1-B. Lachat Instruments, Milwaukee, WI.