Refinement of Weak Acid Dissociable (WAD) Method for Measuring Weak Metal Cyanide Complexes in Aqueous Samples

The primary objective of this study was to correct deficiencies that had been identified in the current weakacid dissociable (WAD) cyanide analytical method. These deficiencies became apparent when the method was applied to groundwater and surface water samples dominated by iron–cyanide complexes (>50% of the total cyanide content); the analytical method, as is, is fine for determining WAD cyanide in any aqueous sample where weak metal cyanide complexes and free cyanide ions dominate the cyanide speciation (i.e., iron–cyanide complexes are <50% of the total cyanide content). It was also determined that the means required to correct these deficiencies depended upon which iron–cyanide complex was present (i.e., ferricyanide/ferrocyanide or an iron–pentacyano methylamino species, [Fe(CN)5NHCH3]4−). For the samples dominated by the ferri- and ferrocyanide complexes, addition of the prescribed amount of zinc acetate under mildly acidic conditions was sufficient to entirely remove these complexes from solution ...