Page 97 - phytochemistry II -pharmD general

Test for purine alkaloids

Murexide test
In a porcelain dish containing about 10 mg of xanthine alkaloid, add 1ml of

conc. HCl and about 10 mg of solid potassium chlorate. Evaporate the mixture to
dryness on a water bath, a yellow residue is left which becomes crimson on further
heating. The color turns purple when residue is exposed to ammonia vapor. The
color is destroyed by solution of fixed alkali.

Separation of purine alkaloids

Separation of mixture of caffeine, theobromine and theophylline depends
on the solubility of caffeine in chloroform or benzene and insolubility of the other
two alkaloids (theophylline and theobromine) in these solvents. Ammonia
solution is then used for isolation of theophylline for theobromine.

Quantitative estimation of purine alkaloids
-Non- aqueous titration.
-Potentiometric.
-Colorimetric methods.

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