Reliable Determination of Cyanide in Treated Water

Abstract

Reliable determination of cyanide in water samples is important for both wastewater and drinking water treatment plant operators and regulatory agencies. However, as a result of cyanide's diverse chemistry, obtaining reliable results has been challenging because several chemical mechanisms can form or destroy cyanide—and some of these can occur within the sample container or during laboratory pretreatment and analysis, leading to biased results. Also, sample matrix constituents or preservation chemicals can interfere with the analytical determination. The US Environmental Protection Agency acknowledged this difficulty for wastewater samples in the 2012 Methods Update Rule by revising the footnote for cyanide preservation to indicate that some interferences may not be mitigated and any technique for removal or suppression of interferences can be used as long as quality control measures are used to demonstrate that the technique worked. Many of the same concerns inherent in testing wastewater apply to testing drinking water. In this study, the effects of holding time, preservation, and on‐line digestion and distillation on cyanide results for wastewater and drinking water were examined, including the use of field dilution as a treatment for interferences and field spikes as a means to gauge whether sample integrity was maintained.