Water Online

November 2017

Water Innovations gives Water and Wastewater Engineers and end-users a venue to find project solutions and source valuable product information. We aim to educate the engineering and operations community on important issues and trends.

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Once all free cyanide is consumed, the excess silver ions react with an indicator (rhodamine, dithiozone, and murexide, for example) that changes color once in contact with free silver ions. However, because silver ions can also remove cyanide from other complexed species, the color might disappear after reaching the actual endpoint, thereby leading to false results. Hence, this well-established method requires experienced users and special analytical equipment, and the reagents needed can have limited bench lifetimes. Corrin-Based Indicators The most recent technology to detect free cyanide relies on its binding to corrin-based indicators. In this case, the indicator not only senses, but also removes cyanide from the solution. A color change of the immobilized indicator, from orange to violet, indicates cyanide's presence in solution. This method allows for naked-eye detection of free cyanide without specialized equipment, organic solvents, and/or toxic substances. The market availability of this technology is limited, but CyanoGuard AG is currently commercializing test kits based on this method. Why Is It Important To Evaluate Your Method Of Choice For Free Cyanide Detection? In many cases, the complexity of your samples might hinder your detection method of choice, leading to false results, unnecessary treatments, and even involuntary disposal of cyanide into surface waters. While most methods perform well in laboratory settings, where the sample composition is known and appropriate equipment is available, their performance might vary in industrial settings. Unfortunately, this is a common situation when testing complex matrices containing known and unknown interfering chemical substances. When using chlorinating agents, ions such as nitrites and sulfides might interfere with the indicator due to their reactivity towards chloramine T. This is a common situation in INSTRUMENTATION 25 wateronline.com n Water Innovations SELECTIVITY SPEED SIMPLICITY SAFETY EQUIPMENT CHLORINATING REAGENTS Low tolerance towards several metal ions, nitrites, sulfides, and thiocyanate 2-15 minutes Experienced users Possible exposure to toxic or harmful substances None and/or dedicated equipment SILVER NITRATE TITRATION Low tolerance towards several metal ions, thiosulfate, and thiocyanate < 15 minutes Experienced users Harmful for the environment; can cause irritation if inhaled Analytical laboratory equipment CORRIN-BASED INDICATORS High tolerance towards most interferences except sulfide < 60 seconds Nonexperienced users Harmless reagents None

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