WWEM - Abstract

Abstract Information :

The analysis of total cyanide in drinking water is required under The Water Supply (Water Quality) Regulations 2018. Total cyanide in drinking water cannot exceed the value of 50 ug/L, its prescribed concentration or value. Samples collected for this analysis must be preserved upon collection with a dechlorinating agent, to prevent the Total cyanide from dissipating as free cyanide, a readily volatile species. Further preservation is also required with NaOH to ensure that any cyanide or cyanide species present are kept in ionic form.

The Systea® analyser is based on the reference method ASTM D7511-09E2 for the analysis of total cyanide by segmented flow injection with in-line UV digestion module and amperometric detection. The digestion allows for the breakdown of complex cyanides into CN- ion, which is captured in a basic acceptor solution. After digestion, the flow is then acidified and the resulting HCN passes through a gas diffusion membrane onto a carrier solution for detection using a silver electrode.

The typically used dechlorinating agents for total cyanide are ascorbic acid or sodium thiosulfate. The first option can lead to false positives in waters disinfected using chloramination, and the latter can interact with the silver electrode used for the detection, creating a positive bias. The method development in the Affinity water laboratory focused on creating a laboratory method that allowed for the use of Thiosulfate as the dechlorinating agent of choice, which was successfully achieved. The method has a working range of 0-20 ug/L, and an estimated limit of quantification within 1-3 ug/L. Preliminary average of recoveries in the various working matrices is 91.6%. The method is currently undergoing validation with a view to be accredited under ISO 17025-DWTS.