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Interlaboratory Study of Free Cyanide Methods Compared to Total Cyanide Measurements and the Effect of Preservation with Sodium Hydroxide for Secondary- and Tertiary-Treated Waste Water Samples

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Several methods exist for the measurement of cyanide levels in treated wastewater,typically requiring preservation of the sample with sodium hydroxide to minimize loss of hydrogen cyanide gas (HCN). Recent reports have shown that cyanide levels may increase with chlorination or preservation. In this study, three flow injection analysis methods involving colorimetric and amperometric detection were compared within one laboratory, as well as across separate laboratories and equipment. Split wastewater samples from eight facilities and three different sampling periods were tested. An interlaboratory confidence interval of 3.5 ppb was calculated compared with the intralaboratory reporting limit of 2 ppb. The results show that free cyanide measurements are not statistically different than total cyanide levels. An artificial increase in cyanide level is observed with all methods for preserved samples relative to nonpreserved samples, with an average increase of 2.3 ppb. The possible loss of cyanide without preservation is shown to be statistically insignificant if properly stored up to 48 hours. The cyanide increase with preservation is further substantiated with the method of standard additions and is not a matrix interference. The increase appears to be correlated with the amount of cyanide observed without preservation, which appears to be greater in those facilities that disinfect their wastewater with chlorine, followed by dechlorination with sodium bisulfite.

Keywords: analytical methods; chlorination/dechlorination; cyanide monitoring; effluent; interlaboratory confidence limits; preservation; treated wastewater

Document Type: Research Article


Affiliations: Department of Chemistry and Biochemistry, California State University San Bernardino, 5500 University Parkway, San Bernardino, CA 92407

Publication date: November 1, 2012

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  • Water Environment Research® (WER®) publishes peer-reviewed research papers, research notes, state-of-the-art and critical reviews on original, fundamental and applied research in all scientific and technical areas related to water quality, pollution control, and management. An annual Literature Review provides a review of published books and articles on water quality topics from the previous year.

    Published as: Sewage Works Journal, 1928 - 1949; Sewage and Industrial Wastes, 1950 - 1959; Journal Water Pollution Control Federation, 1959 - Oct 1989; Research Journal Water Pollution Control Federation, Nov 1989 - 1991; Water Environment Research, 1992 - present.
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