Cyanide has been a long regulated inorganic contaminant in drinking and bottled water in the U.S. and is regulated both by the U.S. EPA and the U.S. FDA Center for Food Safety and Applied Nutrition (CFSAN). In the U.S., the typical source of cyanide is industrial contamination (plating, mining, and the burning of coal and plastics) but in some countries, staple food products such as sorghum, cassava, flax, and bamboo shoots are also sources of cyanide.
The reason cyanide is regulated is because of its toxicity: it interferes with iodine uptake by the thyroid, and chronic exposure to cyanide can result in goiters, some neuron-muscular diseases, and cretinism.
Ion Chromatography (IC) has been an EPA-approved method for determination of total cyanide in water since 2009 when it added ASTM D2036-09 Standard Test Methods for Cyanides in Water, Test Method A Total Cyanide after Distillation. The method measures free cyanides and strong metal-cyanide complexes (e.g., iron cyanides) that dissociate and release free cyanide when refluxed under strongly acidic conditions. As stated in the method:
…Samples are digested with sulfuric acid in the presence of magnesium chloride … After distillation, the cyanide concentration can be determined with… ion chromatography…The inclusion of ion chromatography and gas diffusion separation with amperometric detection as determinative steps (D2036-09, sections 16.5 and 16.6) will give users additional options to measure cyanide after distillation. Furthermore, these determinative steps can be used to mitigate interferences that have been associated with conventional colorimetric test methods.
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I am pleased to share with our readers a recently released poster, Direct Determination of Cyanide in Drinking Water by IC-PAD, (downloadable PDF) discussing the development of an IC method with pulsed amperometric detection (PAD) to directly determine free cyanide in drinking water. This method demonstrates good retention time stability with <1% RSD (140 injections), linear calibration from 2 μg/L to 100 μg/L cyanide (r2 >0.999), and a MDL, measured at three times the noise, of 1.0 μg/L.
We have a comprehensive page on cyanide testing on our website; the Related Literature tab includes a substantial list of analytical methods for cyanide and metal cyanide.
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