Page 18 - Phytochemistry 2 (06-PG 605)

3- Marqui's reagent: Few drops of 40% formaldehyde in conc. H2SO4.
4- Erdmann's reagent: A mixture of conc. HNO3 and conc. H2SO4 in water.
5- Conc. HNO3.

Quantitative estimation of alkaloids

Purposes of Quantitative estimation (assay) of alkaloids :

1. Determination of the total and individual alk. contents of crud drugs & galenicals.

2. Determination of pharmacological potency

3-Distinction of genuine drugs from adulterated ones (partial or complete
exhaustion).
4- For kinetic studies of the rate of deterioration of drugs under various conditions
of storage (stability) e.g. Eserine eye drops.

Different methods used for quantitative determination (Assay) of alkaloids:

1. Gravimetric
2. Volumetric
3. Colorimetric
4. Spectrophotometric
5. Fluoremetric
6. Chromatographic

1- Gravimetric method:

It can be applied by
Direct weighing of the alkaloid:
In this method the total purified alkaloidal extract is evaporated to dryness in
tared container and the residue is further dried till constant weight.

Advantages of Gravimetric method:
1. No interference of volatile bases as they are removed on evaporation of the
solvent.
2. It is not dependent on the formula or molecular weight of the bases (Suitable
for determination of mixture of alkaloids or in the case of the presence of
unknown alkaloid in the drug sample). The final figure obtained is the total
weight of alkaloids present.
3. There is no need for consideration of chemical equivalence, contributions
due to alkalinity of glass, choice of indicator,… etc; as in the case with
volumetric procedures.
4. It is useful for weakly basic alkaloids.

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