The determination of ferrocyanide and related compounds in commercial sodium chloride

Abstract

Ferrocyanide [hexacyanoferrate(II)] in commercial sodium chloride can be determined spectrophotometrically as its iron complex in the range 0·013 to 50·0 p.p.m. of [Fe(CN)₆]^4–. The iron complex is concentrated from a large volume of sample solution by filtration on kieselguhr, and a reproducible Prussian blue colour formed in a small volume under controlled conditions. Aquopentacyanoferrate can be determined simultaneously, and the amounts of each complex present are found by a simple calculation. Some interference is caused by carbonylpentacyanoferrate, which only partially reacts under the conditions of the procedure but the amount present can be determined and allowance made. The precise determination of carbonylpentacyanoferrate is carried out by using a similar principle of concentration, but with different reagents to develop the iron complex. No interference is caused by the presence of other stable iron-cyanogen complexes, or by the usual impurities and additives in commercial salts.