Page 21 - phytochemistry general program

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:

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

Gravimetric method: .1
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:
No interference of volatile bases as they are removed on evaporation of the .1

solvent.
It is not dependent on the formula or molecular weight of the bases (Suitable .2

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.

19