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Mayer’s Test for Alkaloids

  • Botany

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

Mayer’s reagent is an alkaloid precipitating reagent used for the detection of alkaloids in natural products. Most alkaloids are precipitated from neutral or slightly acidic solution by Mayer’s reagent (potassiomercuric iodide solution) to give a cream coloured precipitate. This test was invented by the German Chemist, Julius Robert Von Mayer (1814–1878).

Principle

The positive result of Mayer’s test was confirmed by yellow precipitate. It was expected as a complex of potassium-alkaloid. In the formation of Mayer’s reagent, the solution of mercury (II) chloride was added by potassium iodide and produced a red precipitate of Mercury (II) iodide. The excess of potassium iodide addition introduce to potassium tetraiodomercurate (II) formation. 

Alkaloids consist of nitrogen atoms which have lone pair electrons. The lone pair electrons are examined to form covalent coordinate bonding with metal ion. In alkaloid identification with Mayer reagent, the nitrogen in alkaloids was predicted to react with metal ion of potassium (K+) from potassium tetraiodomercurte (II) producing a complex of potassium-alkaloid precipitating.

Requirements

Materials

  1. Test tube
  2. Test tube stand
  3. Distilled water
  4. Plant sample

Chemicals

  1. Mercuric Iodide
  2. Potassium Iodide

Reagents

  1. Mayer’s Reagent Preparation: This was prepared by measuring 1.3 g of mercuric iodide on a weighing balance and 5.0 g of KI (Potassium Iodide) and dissolving both in distilled water, made up to 100 ml.

Mayer’s Test for Alkaloids Procedure

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

Expected Result

Mayer's Test

Emergence of whitish or cream precipitate implies the presence of alkaloids.

Further Readings

Reference