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Principle of Dragendorff’s Test for Alkaloids

  • Botany

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

Dragendorff’s test reagent is a colour reagent that can be used to identify alkaloids in test samples or as a chromatography plate stain. Alkaloids will react with Dragendorff’s test reagent and form an orange or orange-red precipitate if they are present in the sample solution. Johann Georg Dragendorff (1836–1898), a German pharmacologist, developed this Dragendorff’s test reagent at the University of Dorpat.

Principle

Dragendorff’s test reagent consists of (Nitrooxy) oxobismuthine (BiNO4xH2O), tartaric acid and KI and it is used for the detection of alkaloids. The Tertiary amine is protonated due to the tartaric acid and an ion pair is formed that consists of [BiI4] and [HNR3]+. In dependence of the nature of the tertiary amine (or alkaloid) this ion pair has an orange color.

Requirements

Materials

1. Test tube

2. Test tube stand

3. Plant Sample

4. Vortex

Chemicals

1. Basic Bismuth Nitrate

2. Glacial Acetic Acid

3. Potassium Iodide

Reagent

1. Stock solution: mix bismuth subnitrate (oxynitrate; 1.7 g) with water (80 ml) and glacial acetic acid (20 ml). Add potassium iodide solution (50% w/v, 100 ml). Shake or stir until dissolved. Solution keeps indefinitely when stored in a dark bottle.

2. Working solution: mix the stock solution ODD ml) with glacial acetic acid (200 ml) and make up to volume o litre) with distilled water. Keeps for 2-5 months when stored in a dark bottle.

Procedure

1. 1mL of extract was taken and placed into a test tube. Then 1mL of potassium bismuth iodide solution (Dragendorff’s test reagent) was added and shaken. An orange red precipitate formed indicates the presence of alkaloids in dragendorff’s test.

Expected Result

Dragendorff’s Test

Appearance of orange brown precipitates revealed the presence of alkaloids.

Further Readings

Reference