Page 22 - phytochemistry general program

It is useful for weakly basic alkaloids. .4
Disadvantages of Gravimetric method:

Unsuitable for volatile or thermolabile alk. .1
The alk. residue must be entirely free from .2
any impurities, otherwise they are weighted as alkaloids.
.1
(+ve ) or ( –ve) error ?

The sample must be sufficiently large to
obtain a residue suitable for accurate weighing.

2- Volumetric (Titrimetric methods):

This method depends on titrimetric determination of total nitrogenous bases.
Titration in aqueous medium .1

Titration in aqueous medium is carried out either by direct titration with a standard

acid solution; or indirectly by back titration of the unconsumed standard acid.
Titration in non aqueous medium .1

Glacial acetic acid in perchloric acid and chloroform as solvent is usually used.

Non aqueous titration is suitable for:
Determination of weakly basic alkaloids .1
For alkaloids that are present in small quantities. .2

3- Spectrophotometric assays:

These assays are applied for: .1
Pharmaceutical preparations, ampoules, eye drops, biological fluids (urine &

blood) where the alkaloids to be analyzed are in a very low concentration.
Can be used as a means of making simultaneous analysis of multi- .2

component systems

4- Colourimetric assays:
It can also be used for crude purified drug extracts when a specific colour .3

reaction is available.
The colour reaction should be quantitative. .4

Examples Colourimetric assays
The colour of Ergot alks with p-dimethyl- aminobenzaldehyd .1

The colour of Morphine with Na nitrite / KOH→Rose colour. .1

5- Flourimetric Method:
The flourescence of the alkaloid, when present, is measured at a certain .2

wavelength.
e.g. Quinine & quinidine in an oxygenated acid.

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