Detection of cyanide

Qualitative Estimation of Cyanide in Biological and Plant Material
Aim
To detect cyanide in biological material (copper-guaic test)
Principle
Acidification of biological fluids liberates cyanide, which interacts with suitable reagents on the filter paper to form chromophores.
Materials and chemicals
Tartaric acid, copper sulphate, alcohol, guaiacol, filter paper, 100 ml flask, heater.
Procedure
1.Take 50 g of finely ground tissue or stomach contents in a 100 ml flask and acidify contents with tartaric acid.
2. A filter paper previously moistened with 10 per cent of guaiacol in alcohol and 0.1 per cent of aqueous copper sulphate solution.
3. Plug the mouth of flask and warm gently.
4. Allow it to stand for 30 minutes.
5. Observe the colour of paper.
Inference
If cyanide is present, a blue colour is developed.

Sodium picrate paper test to detect cyanide in plant sample
Aim
To detect the presence of cyanide in the given plant sample.
Materials and chemicals
Sodium bicarbonate, picric acid, filter paper, distilled water, chloroform, test tube, spirit lamp.
Preparation of sodium picrate paper
Dissolve5 g sodium bicarbonate and 0.5 g picric acid in 100 ml distilled water, cut filter paper into strips of 2" x6" size. Dip the strips in the reagent and dry in cool place.
Test procedure
1.Take the given sample in a test tube and add few drops of water and chloroform.
2. Plug the test tube with cotton, hanging the dried picrate paper. The paper should not touch the fluid in the tube.
3. Heat the tube gently till fumes evolve.
4. Observe the colour of paper.
Inference
If the colour of paper changes from yellow to brown it indicates that the plant sample is positive for cyanide.
The leaves and stomach contents are to be frozen immediately after collection in a polythene bag as cyanide is likely to evaporate.

Scheerer's test for detecting cyanide.
Materials and chemicals:
10% tartaric acid, a strip of filter paper dipped in a saturated solution of picric acid, dried and soaked in 10% sodium carbonate or sodium hydroxide at a concentration of 2 mol/L.
Method.
Place a small amount of the suspected material into a wide test-tube or conical flask and add tartaric acid. Fix the filter paper in the neck of the tube or flask and seal the neck.
Inference: If hydrogen cyanide is given off, the paper turns pink or red