Chloride is extracted by shaking 10 g of air dry soil and 25 mg of charcoal in 30 mL of 0.01 M CaSO4 for 30 minutes. Samples are subsequently centrifuged or filtered and analyzed on a Lachat QuikChem 8500 Flow Injection Analyzer by the mercury (II) thiocyanate method. In this method, chloride sequesters mercury from mercuric thiocyanate thereby liberating thiocyanate ion. The thiocyanate ion forms reddish yellow colored ferric thiocyanate in the presence of excess ferric nitrate, which is measured colorimetrically at 480 nm.
(See Method References No. 13 & 14)