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