Chemical test for cyanide

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[edit] Prussian blue

The formation of Prussian blue can be used as a test for inorganic cyanide, for instance in the sodium fusion test.

Iron(II) sulfate is added to a solution suspected of containing cyanide, such as the filtrate from the sodium fusion test. The reslting mixture is heated for a few minutes, cooled, and acidified with mineral acid.

The formation of Prussian blue is a positive result for cyanide.

[edit] para-benzoquinone in DMSO

An alternative test for cyanide is to use a solution of para-benzoquinone in DMSO this reagent when treated with cyanide will form a fluorescent compound. The cyanide acts as a nucleophile on the benzoquinone to form a cyanophenol. Use a UV light to see the green/blue glow which will be present if the test is positive.

[edit] Copper and an aromatic amine

This test has been used in the past by fumigators to detect hydrogen cyanide.

A copper(II) salt and an aromatic amine such as benzidine is added to the sample, as an alternative to the benzidine an alternative amine di-(4,4-bis-dimethylaminophenyl) methane can be used. If the test is positive a blue colour will appear. Warning Benzidine is a very nasty carcinogen, as are some of the other amines which can be used for this test.

Copper(I) cyanide is very insoluble. By sequestering the copper(I) the copper(II) is rendered a stronger oxidant. The copper, in a cyanide facilitated oxidation, converts the amine into a coloured compound. The Nernst equation explains this process. Another good example of such chemistry is the way in which the saturated calomel reference electrode (SCE) works. The copper, in a cyanide facilitated, oxidation converts the amine into a coloured compound.