False positives for cyanide analysis in wastewaters have been reported. We examined the effects of storage time at high pH and of pH adjustments on the cyanide levels. Cyanide levels changed within the holding time allowed by Standard Methods. We also studied the difference in cyanide levels using two disinfection conditions --breakpoint chlorination and chloramination. Glycine was used as the precursor to study the cyanide formation pathways. Under breakpoint chlorination conditions, cyanide formation is complete relatively quickly and detectable cyanogen chloride is produced. On the other hand, chloramination yields cyanide through a relatively slow, base-catalyzed reaction. Chloramination followed by dechlorination with sodium arsenite and addition of NaOH results in cyanide levels that increase significantly upon reanalysis in the first 24 hours and then remain relatively constant after that time. Cyanogen chloride (CNCl) was <5 ppb in samples disinfected with chloramination. Mechanisms are proposed that explain the very different cyanide results that are obtained when disinfection is carried out under breakpoint chlorination conditions versus chloramination conditions.

Dechlorinating agents and pH adjustment are often used to preserve wastewater samples for cyanide analysis. The effects of four approved preservation protocols on the results of the total cyanide analysis of effluents from four Water Reclamation Plants (WRPs) were examined. The results differed widely, and a clear pattern emerged. Immediate analysis without pH adjustment generally gave total cyanide concentrations below the reporting limit of 5 µg/L, irrespective of the dechlorinating agents used. When the pH was adjusted to ≥ 12, a slight increase in the measured total cyanide concentration was observed when thiosulfate was used to dechlorinate the samples, and a significant increase (> 10 µg/L) was observed when arsenite was used as the dechlorinating agent. These results provide evidence that approved preservation protocols may give rise to cyanide formation in chlorinated wastewater effluent matrices.

Dechlorinating agents and pH adjustment are often used to preserve samples for the total cyanide analysis of wastewater samples. We examined the effects of four approved preservation protocols on the results of the total cyanide analysis of the effluent from four publicly owned treatment works (POTWs). The results differed widely, and a clear pattern emerged. Immediate analysis without pH adjustment to ≥ 12 gave cyanide concentrations below our reporting limit of 5 µg/L, irrespective of the dechlorinating agents used. When the pH was adjusted to ≥ 12, a slight increase in the measured cyanide concentration was observed when thiosulfate was used to dechlorinate the samples, and a significant increase (> 10 µg/L) was observed when arsenite was used as the dechlorinating agent. These results provide evidence that approved preservation protocols may give rise to cyanide formation in chlorinated wastewater effluent matrices.