Contents
- Introduction
- Colour Tests
- Ammonium Molybdate Test
- Cobalt Thiocyanate Test
- Copper Sulphate – Pyridine Test
- Dille – Koppayani Test
- Duquenois Levine Test
- Ferric Chloride
- Ferricyanide Test
- Fujiwara Test
- FPN Test
- Fuchsine Test
- Gerrard’s Test
- Gunzberg’s Test
- Gutzeit Test
- Liebermann’s Test
- Prussian Blue Test
- Mandelin’s Test
- Marsh’s Test
- Marquis Reagent Test
- McNally’s Test
- Mecke Test
- Reinsch Test
- Simon’s Test
- Trinders Test
- Zwikker’s Test
- References
Introduction
The detection of poisons through color tests is a fundamental aspect of forensic and analytical chemistry. These tests rely on the unique chemical reactions between toxic substances and specific reagents, resulting in characteristic color changes. By harnessing the principles of chemical reactivity and colorimetry, analysts can swiftly identify the presence of various poisons in diverse samples.
Color tests offer a rapid and reliable means of screening for poisons, enabling investigators to gather crucial evidence in cases of suspected poisoning. From detecting alkaloids to identifying heavy metals, these tests cover a wide range of toxic compounds encountered in forensic investigations and toxicology analyses.
Colour Tests
1. Ammonium Molybdate Test
Procedure: Add Ammonium Molybdate and Nitric Acid to extract, observe for yellow crystalline precipitate on boiling.
Observation: Formation of yellow crystalline precipitate.
Result: Distinction from Arsenites and Phosphates.
2. Cobalt Thiocyanate Test
Procedure: Dissolve 0.38 gram of ammonium thiocyanate in 25 ml water, and then slowly add 0.63 gram cobaltous acetate with stirring.
Observation: observe the colour
Result:
- PCP – blue
- Cocaine – blue
3. Copper Sulphate – Pyridine Test
Procedure: Add 1 ml of extract to a dilute solution of Copper Sulphate with Pyridine and observe for a lilac-blue precipitate.
Observation: Formation of a lilac-blue precipitate.
Result: Presence of Cyanate.
4. Dille – Koppayani Test
Procedure: Mix extract with Cobalt Acetate and Isopropylamine solutions, observe for purple or blue violet colour.
Observation: Appearance of purple or blue violet colour.
Result: Presence of Barbiturates.
5. Duquenois Levine Test
Procedure:
- Step I- Small amount of suspected residue of extract is placed in a test tube and shaken with 2ml of duquenois reagent for one minute.
- Step II- 2 ml of Conc. Hydrochloric acid is added.
- Step III-Shaken and allowed to stand for 10 Minutes
- Step IV-Add 2ml chloroform if a color develops.
Observation: Violet
Result: Cannabis
6. Ferric Chloride
Procedure: Dissolve 1.5 grams of ferric chloride in 29.0 milliliters of water.
Observation: Observe the colour
Results:
- Acetaminophen – violet-purple
- GHB – red/brown
7. Ferricyanide Test
Procedure: To 50 ml of filtered stomach contents or scene residue add 100ml of aqueous hydrochloric acid(2 mol/L) and 50ml of aqueous potassium ferricyanide solution (10 gm/l). To a further 50 ml of sample add 100 ml of hydrochloric acid and 50ml potassium ferrocyanide solution (10gm/l).
Observation: A deep blue precipitate with Potassium Ferricyanide indicates the presence of ferrous.
Result: Ferrous
8. Fujiwara Test
Procedure: Dilute 1ml of sample with 2ml of Sodium Hydroxide solution
Observation: Blue
Result: Cyanide
9. FPN Test
Procedure: 5ml of ferric chloride solution. 45ml of 20% solution of perchloric acid and 50 ml of 50% solution of nitric acid is added to make a final solution.
Observation: Color Ranging from pink to red, orange, violet or blue
Result: Phenothiazines
10. Fuchsine Test
Procedure: Place 1 drop of Fuchsine reagent on a spot plate, add neutral extract solution, and observe for discharge of magenta colour.
Observation: Discharge of magenta colour.
Result: Presence of Sulphites.
11. Gerrard’s Test
Procedure: 1-2 ml of 2% Mercuric chloride solution in 50% of alcohol is added to a portion of residue of the extract.
Observation: Red
Result: Hyoscyamine
12. Gunzberg’s Test
Procedure: Evaporate Gunzberg’s reagent to dryness, add material to be tested, warm gently, and observe for purplish red colouration.
Observation: Formation of purplish red colouration.
Result: Presence of free Hydrochloric Acid.
13. Gutzeit Test
Procedure: Take 1 ml of solution into a Gutzeit apparatus. Add 2 pellets of pure Zinc metal and 5 ml of dilute Sulphuric Acid. Purify the evolved gas by passing over Lead Acetate paper and react with Mercuric Chloride test paper.
Observation: Yellow stain on the paper.
Result: Presence of Arsenic.
14. Liebermann’s Test
Procedure: Evaporate alkaline distillate to dryness, add Sodium Nitrite, then concentrated Sulphuric Acid, and observe for colour changes.
Observation: Colour changes indicating presence of specific compounds.
Result: Presence of specific compounds such as Phenol, Resorcinol, Alpha naphthol, Beta-naphthol, Cresols, and p-Amino-phenol.
15. Prussian Blue Test
Procedure: Mix extract with freshly prepared Ferrous Sulphate solution, add Hydrochloric acid, and observe for a blue colouration or precipitate.
Observation: Blue colouration or precipitate.
Result: Presence of Cyanide.
16. Mandelin’s Test
Procedure: Add Mandelin’s reagent to residue, observe for deep violet-blue or deep purple colour turning to yellow.
Observation: Appearance of deep violet-blue or deep purple colour turning to yellow.
Result: Presence of Strychnine.
17. Marsh’s Test
Procedure: Boil the solution with pyrogallol and sulphurated water to reduce pentavalent Arsenic to trivalent state. Perform the test in a Marsh apparatus and observe for a mirror of black metallic lustre.
Observation: Black metallic lustre mirror.
Result: Detection of minute traces of Arsenic.
18. Marquis Reagent Test
Procedure:
- Step I- prepare a marquis reagent first by adding 3ml of conc. Sulphuric acid and 3 drops of formalin.
- Step II- place a Drop of Marquis Reagent on the sample.
- Step III- Observe the colour
Result:
- Opiates (heroin, oxycodone) – purple
- Phenethylamines (meth)amphetamine – orange/brown
- MDA/MDMA – purple/black
- Aspirin – slow cherry red
19. McNally’s Test
Procedure: Add Acetone, water, Copper Sulphate solution with Acetic Acid, and Sodium Nitrite. Heat and observe for red colouration.
Observation: Formation of red colour.
Result: Presence of Salicylates or Salicylic Acid.
20. Mecke Test
Procedure:
- Step I: This color test reacts with a wide range of aromatic compounds to produce colored intermediates.
- Step II: Add 0.25 grams of selenious acid to 25 milliliters of concentrated sulfuric acid with stirring.
Observation: Observe the color
Results:
- Bufotenine – brown to black/purple
- Diphenhydramine HCl – yellow
- Heroin HCl – green/blue
- Hydrocodone bitartrate – dark blue
- Methadone – green/brown
- MDMA – green to dark blue
- MDA – green to blue
21. Reinsch Test
Procedure:
- Step I- take a copper wire and clean it with nitric acid until it gets a bright surface.
- Step II- Rinse the cleaned copper wire with purified water.
- Step III- Add 10ml of conc. Hydrochloric acid and 20ml of test solution in 100ml conical flask.
- Step IV- Heat on a boiling waterbath in a fume cupboard for 1 hour.
- Step V- Maintain the volume of solution by adding dilute hydrochloric acid as necessary.
Observation: Color staining on copper can be interpreted as follows:
Result:
- Copper Black-Antimony
- Dull Black-Arsenic
- Shiny Black-Bismuth
- Silver Color-Mercury
22. Simon’s Test
Procedure:
- Step I- Reagent A: 1 % Sodium Nitroprusside/10 % by Volume of Acetaldehyde
Dissolve 1 gram of sodium nitroprusside in 100 milliliters of water, then discard 10 milliliters of this solution. Add 10 milliliters of acetaldehyde to the remaining 90 milliliters of sodium nitroprusside/water.
- Step II- Reagent B: 2 % Sodium Carbonate
Dissolve 2 grams of sodium carbonate in 100 milliliters of water.
- Step III- Place a small amount of sample in a culture tube or clean spot well and add one drop of Reagent A, then add 2 drops of Reagent B.
Observation: Observe any reaction or color.
Result:
- Methamphetamine and secondary amines – blue-violet
- Amphetamine and primary amines – Negative reaction (light pink is the color of the reagent.)
23. Trinders Test
Procedure: Add 100ml of trinders reagent to 2 ml urine and mix for 5 seconds.
Observation: Violet
Result: Salicylate
24. Zwikker’s Test
Procedure: Take up the residue of extract in Chloroform, add Pyridine, and observe for colour change.
Observation: Colour change from purple to weak blue or green.
Result: Presence of Thiobarbiturates or non-Thiobarbiturates.
Forensic Toxicology and Sample Testing
References
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- Clarke, E.G.C. and R.G. Todd, eds. Isolation and Identification of Drugs. 1st Edition. London: Pharmaceutical Press, 1969, 129-130, 1183.
- Feigel, Fritz. Spot Tests in Organic Analysis. Elsevier Publishing Co.: 1956, 251.
- Fulton, C.C. Modern Microcrystal Tests for Drugs. New York: Wiley-Interscience, 1969, 336.
- Kumari Anupama, et al. “Test For Detection Or Identification Of Poison,” wjpmr, 2020,6(10), 58-60
- Sobol, S.P. and R.A. Moore. Analytical Manual, J.W. Gunn, ed. Bureau of Narcotics and Dangerous Drugs, Washington, D.C.: U.S. Government Printing Office 0-506-836, 1970: 105.
- Johns, S.H. “Spot Tests: A Color Chart Reference for Forensic Chemists.” Journal of Forensic Sciences, Volume 24. Issue 3 (July, 1979): 631-649.
- Jungreis, Ervin. Spot Test Analysis – Clinical, Environmental, Forensic, and Geochemical Applications, New York: John Wiley & Sons, 1985, 80.
- Poyner, B. et al. “Presumptive Color Test for Synthetic Cannabinoids Containing an Indole Substructure.” Journal of the Clandestine Laboratory Investigating Chemists Association. Volume 22 Number 4 (Oct. 2012): 27-31.
- Liu, Ray H. and Daniel E. Gadzala. Handbook of Drug Analysis: Applications in Forensic and Clinical Laboratories. Washington, D.C.: American Chemical Society, 1997: 58.
- Toole, K.E. et al. “Color Tests for the Preliminary Identification of Methcathinone and Analogues of Methcathinone.” Microgram Journal, Volume 9, Number 1 (Jan. 1999): 27-32.
