Page 65 - phytochemistry II -pharmD general

% of atropine = A - (B+C)

Quantitative determination of solanaceous alkaloids.

A vast number of techniques have been used for the evaluation of the
tropane alkaloids in plant extracts and as pure compounds. These techniques
involve volumetric, colorimetric, photometric, potentiometric, acid-dye and
immunoassay techniques.

A combination of extractive procedures and chromatographic separation
would allow the determination of alkaloids with a minimum percentage of error.

Assay of Hyoscyamus niger leaf (B.P. 1998)

Definition

Hyoscyamus leaf consists of the dried leaf or the dried leaf and flowering,
and occassionally fruit- bearing, tops of Hyoscyamus niger L. It contains not less
than 0.05 percent of total alkaloids, calculated as hyoscyamine (C17H23NO3, M wt
289.4) with reference to the drug dried at 100 0C to 105 0C. The alkaloids consist
mainly of hyoscyamine with varying proportion of hyoscine (scopolamine).

Principle of assay

1- Total alkaloids are liberated by maceration with a mixture of alcohol, ether and
ammonia.

2- Extraction is carried out by percolation with ether, chloroform mixture.

3- Total alkaloids are determined volumetrically by adding a known volume of
standard acid to the purified alkaloid residue and then back titration of the
excess acid with standard alkali.

Estimation of pure alkaloids

Pure alkaloids are evaluated by:

1- Colorimetric method
Atropine gives violet colour with Vitali-Morine’s reagent. The colour can be

measured colorimetrically at a wavelength of 550 nm.

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