Dragendorff's reagent

Alkaloids, if present in the solution of sample, will react with Dragendorff's reagent and produce an orange or orange-red precipitate.

[1] This reagent was invented by the German pharmacologist, Johann Georg Dragendorff (1836–1898) at the University of Dorpat.

Many compositions degrade over time and are sensitive to light, so for long-term storage it is often prepared as two separate solutions to be mixed before use, one containing bismuth subnitrate and acid with the other containing potassium iodide.

The most common composition is as follows: Part A: 0.85g bismuth subnitrate, 40mL water, and 10mL glacial acetic acid.

This ion pair has different colors: yellow, orange, red, and brown, which depend on the nature of alkaloids.