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Wagner’s Reagent Test for Alkaloids

  • Botany

In this wagner’s reagent test for alkaloids post we have briefly explained about wagner’s test principle, requirements, procedure, and wagner’s test expected result.

Wagner’s Reagent Test for Alkaloids

Alkaloids are a class of basic, secondary plant substances that usually have a hetero-cycle including nitrogen. This trait gives them their basic personality. The alkaloids are generally colourless crystalline solids that are non-volatile. They are water insoluble but soluble in organic solvents such as ethanol, ether, benzene, chloroform, and others.

Principle

Wagner’s test iodine reacts with I- ion from potassium iodide producing I3- ion (brownish solution). In the Wagner’s test, the metal ion of K+ will bind as covalent coordinate bonding with nitrogen to alkaloid producing a complex precipitate of potassium-alkaloid.

Requirements

Materials

  1. Test tube
  2. Test tube stand
  3. Plant Sample
  4. Vortex

Chemicals

  1. Mercuric chloride
  2. Potassium Iodide

Reagents

Wagner’s reagent : Wagner’s test reagent (reagent for alkaloids) that prepared by Dissolve 2 g of iodine and 6 g of KI in 100 ml of water.

Procedure

1mL of extract was taken and placed into a test tube. Then 1mL of potassium mercuric iodide solution (Wagner’s test reagent) was added and shaken. Emergence of whitish or cream precipitate implies the presence of alkaloids.

Expected Result

wagner test

Appearance of reddish brown precipitate signifies the existence of alkaloids an positive Wagner’s test result. Image describes existence of alkaloids and absence of alkaloids.

Further Readings

Reference