Wastewater derived interferences in cyanide analysis

Common, cellulose-derived and other naturally occurring organics which are likely to be present, or generated in wastewater discharges were evaluated. During cyanide analyses, reactive organic compounds produced CN− in samples containing oxidized nitrogen ions. The study showed that oxidized nitrogen species (NO−2 and NO−3) can be generated when hypochlorite or hydrogen peroxide is added to ammonia solutions. Under the conditions existing during cyanide analysis, nitrate and nitrite ions are converted to nitric and nitrous acid respectively. These acids react with organic molecules present in solution to form intermediate oximes, nitro-alkanes, hydroxamic acids and other transient compounds which are unstable in hot, strongly acidic environments. The thermally oxidatively labile intermediates break down to produce CN− and other degradation products. Some condensation of nitrogen oxides with organics in solution may occur prior to distillation, since addition of sulfamic acid to samples in the study did not completely eliminate all cyanide formation. The formation of these labile intermediates is greatly reduced, however, when NOx is removed by sulfamic acid prior to distillation. This study revealed the general nature of these cyanide forming reactions with common hydroxyl, poly-hydroxyl, aldehyde, ketone and other functional groups.