Chloride is extracted by shaking 300 mg of dried plant material with 30 mL of 0.01M CaSO4 solution for 30 minutes. Add 0.85cc of pre-washed charcoal to each sample and continue shaking for 5 additional minutes. Centrifuge for 20 minutes and/or filter (Whatman No. 42). An aliquot is analyzed colorimetrically by the mercury (II) thiocyanate method. In this method, a reddish yellow-colored complex of ferric thiocyanate is formed when chloride ions sequester the mercury ions of mercuric thiocyanate (thereby freeing the thiocyanate) in the presence of excess ferric nitrate. The color is measured on a Lachat 8500 FIA at 480 nm.
(See Method References No. 56 and No. 43)