PICRATE TEST FOR THE PRESENCE OR LIBERATION OF CYANIDE
(From:Burrows GE and Tyrl RJ. Toxic Plants of North America 2001 Iowa State Press, Ames, Iowa)
Preparation of Paper Test Strips
1. Cut filter paper into strips measuring 1 cm/5 cm
2. Dissolve 0.5 g picric acid and 5 g sodium bicarbonate in 100 ml distilled water
3. 3. Dampen ½ of each strip in the solution and allow to dry.
4. Store the strips in a dark, airtight container, and keep container cool. The strips should be usable for 1 year when stored in these conditions.
The Test
1. Cut or shred enough leaf material to fill the bottom 1/3 of a 15-30 mL test tube.
2. Add a few drops each of chloroform and water
3. Suspend a strip of the prepared filter paper from the top of the tube so that it does not touch the leaves, and stopper the tube tightly
4. Hold the tube vertically in the hand or place it in warm (37C) water for up to 2 hours.
Interpretation of Results
1. If HCN is released from the leaves, the yellow filter paper will turn brick red
2. The rapidity of the change is indicative of the intoxication potential
3. The potential is high if the color change occurs within 10 minutes of the beginning of the test.
4. The potential is minimal if little or no color change is apparent within 60-120 minutes
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