Dragendorff's reagent is a color reagent to detect alkaloids in a test sample or as a stain for chromatography plates.DR is a solution of potassium bismuth iodide composing of basic bismuth nitrate (Bi(NO₃)₃), tartaric acid, and potassium iodide (KI), and when contact with alkaloids DR produces an orange or orange red precipitate.

The Dragendorff reagent has two solutions. One is bismuth nitrate in acetic acid. This is followed by a sodium nitrate solution. Alkaloids are indicated by a reddish-brown deposit.

Dragendorff's reagent is prepared by mixing a concentrated solution of potassium iodide with a solution of bismuth subnitrate in a diluted acid  as a low pH is mandatory for this reagent.

DRAGENDROFF S REAGENT