CHEMICAL TESTS FOR ALKALOIDS

 

The chemical tests used for detection of alkaloids depend on their character to precipitate with  organic  acids  in  the  form  of  their  salts.  

These  are  also  precipitated  by  the  reaction  of compounds of   heavy metals like mercury, gold, platinum etc. 

Caffeine and some other alkaloids which are highly water soluble, do not give the tests with usual reagents. 

  Reagents used for the detection of alkaloids

S.No	Name of reagent	Chemical composition	Colour obtained	Example
1	Mayer’s reagent	Potassium mercuric iodide   solution	Cream	Common
2	Wagner’s reagent	Solution of iodine in potassium   iodide	Reddish-brown	Common
3	Dragendorff’s   reagent	Potassium bismuth iodide   solution	Reddish-brown	Common
4	Hager’s reagent	Saturated solution of picric acid	Yellow	Common
5	Picrolonic acid	Solution of picrolonic acid	Yellow	Common
6	Tannic acid	Solution of tannic acid		Common
7	Murexide test	*Potassium chlorate+HCl+NH3	Purple	Caffeine
8	Mineral acids	Phosphotungstic acid,   phosphomolybdic acid	Yellow	Colchicine
9	Acidic p-methyl-   aminobenzaldehyde	p-Methyl-aminobenzaldehyde   and sulphuric acid	Bluish-violet to   red	Indole
10	Nitric acid	Dilute nitric acid	Orange-red	Morphine