Colour Spot Test
Definition
A presumptive identification reaction in which a small amount of concentrated fraction is treated with a chromogenic reagent (Marquis, Mecke, Mandelin, Mayer, Dragendorff, Wagner) on a white spot tile. The colour produced narrows the drug class before TLC and instrumental confirmation.
- Type
- Presumptive drug identification test
- Common reagents
- Marquis, Mecke, Mandelin, Mayer, Dragendorff, Wagner
- Equipment
- White spot tile
- Role in workflow
- Narrows drug class before TLC and instrumental confirmation
Common questions
Why can a colour spot test never be used as final confirmation of a drug's identity?+
Colour reactions are presumptive because different compounds, and even some legal substances, can produce similar colour changes with the same reagent, so a positive result only narrows the possibilities and must be followed by a confirmatory instrumental method such as GC-MS.
What causes a colour spot test to give a false or ambiguous result?+
Contaminants or cutting agents mixed with the drug can alter or mask the expected colour reaction, and some reagents degrade with age or exposure to light, so laboratories run reagent blanks and known standards alongside casework samples to catch these issues.
Related terms
- Ammonium Sulphate Modification
- The Otto variant in which saturated (NH4)2SO4 is added to a protein-rich homogenate (liver, kidney, blood) to salt out proteins before partitioning....
- Defatting
- A clean-up step before partitioning in which the acidified aqueous is washed with petroleum ether or n-hexane to remove fats, waxes and...
- Fraction a
- The acidic ether extract obtained by partitioning the acidified aqueous tissue digest with diethyl ether at pH 2 to 3. Contains barbiturates,...
- Fraction B
- The alkaline chloroform extract obtained after basifying the residual aqueous to pH 9 to 10 with ammonium hydroxide and partitioning with chloroform....
- Stas-Otto Method
- Sequential acid-alkaline solvent partitioning that isolates organic poisons from biological matrix in two fractions: acidic ether (Fraction A) for acidic and neutral...