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Amenable Cyanide, Total Chlorinated Cyanide analysis problem

I am working with a cyanide sample and determining the amenable CN. When I add calcium hypochlorite to the sample and then distill it and color with chloramine T and pyridine barbituric acid process, I am getting a higher CN result for the total chlorinated treated than the total CN on the same sample. This doesn't make sense because I can't be creating more CN. Are there some interferences that I am bringing out at the same wavelength? Is it possible that in the chlorination process, I am removing interferences that might be giving me a lower value in the total analysis? The amenable CN is the amount in question and therefore because the amenable is the amount from the chlorinated process subtracted from the total amount, my result is negative but it is greatly negative because of the huge difference in the total chlorinated process.

Kyle McKee
Lab Tech - Dallas, Texas
September 16, 2009

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September 21, 2009

I've seen this phenomenon many times. I believe it to be due to the chlorine destroying some of the many poorly understood interferences with this analysis, some of which there is no way of compensating for.

You might try doing "Weak and Dissociable Cyanide", where the distillation is done under much milder coniditions and the aforementioned interferences have much less effect.

Dave Wichern
Consultant - The Bronx, New York

It is very possible to generate CN during the chlorination process of the CATC test. A possible scenario is the presence of SCN,and NH4. When you chlorinate the sample, and spin it the chlorine combines with ammonia ⇦this on eBay or Amazon [affil links] to create chloramine. Chloramine then reacts with SCN and generates CN. This is but one reaction that generates cyanide during the chlorination step. Other compounds, such as organonitrogens (proteins, etc) can do this as well. OIA1677 was created specifically because the CATC method does not work. Besides the formation of CN during the chlorination half of the CATC there are multiple interferences during the total distillation process as well. These potential reactions can create and/or destroy cyanide all at the same time. Basically, when running the CATC test you can never have any confidence that the numbers obtained are real. Why even do this test when an interference free method that takes minutes instead of hours is approved, available, and obtains better detection limits and precision?

Wuilliam Lipps
- College Station, Texas, USA
September 27, 2009

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SCN- reacts with chloramine T to produce cyanogen chloride, not cyanide. I suppose that some could dissolve in the sparger solution to give a positive test.

One might wait a few minutes, in the colorimetry, after the addition of the phosphate buffer, to see if the CNCl hydrolyzes to cyanate. This reaction takes place much faster at lower pH values.

To the best of my knowledge, CNCl cannot go back to cyanide.

Dave Wichern
Consultant - The Bronx, New York
September 29, 2009