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 solution |
Cream |
Common |
2 |
Wagner’s reagent |
Solution of iodine in potassium iodide |
Reddish–brown |
Common |
3 |
Dragendorff’s reagent |
Potassium solution |
Reddish–brown |
Common |
4 |
Hager’s |
Saturated solution of picric acid |
Yellow |
Common |
5 |
Picrolonic acid |
Solution of picrolonic acid |
Yellow |
Common |
6 |
Tannic acid |
Solution of tannic |
|
Common |
7 |
Murexide test |
*Potassium chlorate+HCl+NH3 |
Purple |
Caffeine |
8 |
Mineral |
Phosphotungstic acid, phosphomolybdic acid |
Yellow |
Colchicine |
9 |
Acidic p–methyl- aminobenzaldehyde |
p–Methyl-aminobenzaldehyde and sulphuric |
Bluish–violet to red |
Indole |
10 |
Nitric acid |
Dilute nitric acid |
Orange-red |
Morphine |