Of course, for research purposes column chromatography using ion-exchange resins have been used successfully and effectively to strip the plant materials of their alkaloidal contents. However, in the commercial scale large volumes of aqueous extracts of plant materials are normally pumped through huge metallic columns packed with cationic resins, which in turn pick up all basic components cations.
Subsequently, the alkaloids i. The column having the cationic resins can be reused once again for the next drug substances. By the advent of the latest separation techniques and the copious volume of informations accumulated through the intensive and extensive research carried out with regard to the conventional processes essentially associated with the separation as well as isolation of the hundreds of alkaloids from the natural plant sources, the following five steps are most important and vital, namely:.
All these five steps shall be discussed individually as under:. The first and foremost step is the sample preparation. The plant material is reduced to a moderately coarse powder by appropriate means using grinders and sieves, to facilitate maximum effective contact of the solvent with the ruptured alkaloid bearing tissues and cells. In the case of plant substances that are rich in oils and fats, such as: seeds, kernels, these non-alkaloidal chemical components need to be eliminated completely by extraction with a suitable non-polar solvent like nhexane, light petroleum ether, in a soxhlet apparatus, which would not extract the alkaloids in question.
However, it is always advisable to shake the light-petroleum ether or n-hexane fraction with a dilute mineral acid and subsequently test the acidic solution for the presence of alkaloids. It has been observed that the alkaloids invariably occur in the plant sources as the salt of acids, such as: oxalates, tannates etc.
Therefore, when the plant substance is exposed to an alkaline medium, the alkaloidal salts are readily converted to the corresponding alkaloid bases. Choice of Alkali Indeed, the choice of a suitable mineral base alkali for the ease of liberation of the alkaloid from the salts is not only very vital but also equally significant and largely depend on the following factors, namely:. Likewise, the corresponding salt of a weakly basic alkaloid and a relatively weak organic acid shall require a rather weaker base for its cleavage.
These alkaloids normally get solubilized while in contact with a strong alkali and, therefore milder alkaline reagents e. In such cases, it is always preferred to defat the plant substance before proceeding for the liberation of free alkaloids. Ammonium Hydroxide Solution Dilute aqueous ammonium hydroxide solution is one of the choicest alkali most frequently used for the liberation of alkaloids from the plant sources. It enjoys a two-fold advantage.
First, being its adequate alkalinity to liberate most of the common alkaloids, and second by, its volatile nature so that it may be removed by evaporation of the solvent. As it has a tendency to be extracted by solvent ether from the aqueous solution, therefore, it is almost necessary to get rid of it by evaporation and subsequent washing repeatedly. In normal practice, usually even the last traces of ammonia are removed when the combined ethereal extract is reduced to half of its original volume under vacuum.
In certain typical instance even the use of KOH or NaOH fails to cleave the tannate salts because of their intimately strong bondage with the alkaloid and extremely insoluble nature. Hence, NaOH solution is strong enough to cause on effective split of the alkaloidal salts. It also acts to control the solubility of the water-soluble pomegranate alkaloids by preventing their dissociation.
The extraction of alkaloidal base may be accomplished by three different types of solvents that are discussed below, namely:. The usual pretreatment of the crude drug with alkali may be avoided completely, because alcohol appears to affect dissolution of not only the alkaloidal salts but also the free bases found in the plant substances. It is, however, believed that alcohol predominantly exerts a hydrolyzing effect upon the alkaloidal tannates and other salts.
In actual practice, neither pretreatment of the crude drug with an alkali nor acidification of the alcohol with a small amount of a mineral acid or an organic acid is required. The penetration and hence the subsequent extraction of the crude drug is almost complete with the help of four successive extractions with an alcohol.
Further, the loss of solvent is comparatively less than the chlorinated solvents e. The extraction of total alkaloids with alcohol is highly recommended because of its maximum efficiency and economical viability.
Interestingly, chloroform is regarded as the choicest water-immiscible solvent for a broad-spectrum of alkaloids present in the plant kingdom and extracts them with varying degrees of ease. Note: Chloroform is not suitable for the extraction of quaternary alkaloids e. Undoubtedly, water being an excellent and absolutely inexpensive polar solvent for the extraction of alkaloids, but if offers an enormous volume of disadvantages because it carries along with it a large number of other plant components, for instance: sugar, pigments e.
Hence, its usage has been resulting to a bear minimum level. In general, the alkaloids may be extracted by any of the following three well-defined and widely accepted processes, namely:. All these three processes shall now be discussed briefly in the sections that follows:. In this instance, the powdered drug is usually moistened with dilute ammonia solution and then packed loosely in the thimble of the Soxhlet apparatus; and the organic solvent affords a deep penetration of the moist drug thereby allowing the greatest possible extraction of the alkaloids from the exposed surfaces of the cells and tissues of the crude drug.
Once, the extraction is ascertained to have completed, the solvent is filtered and evaporated in a Rotary Thin-Film Evaporator and the residue is treated further for the isolation of individual alkaloids. The proportion of crude drug to solvent should be maintained as 1 Kg to 1 L. If any alkaloid is removed by the petroleum ether, it must be recovered by treating it with dilute mineral acid. This document was uploaded by user and they confirmed that they have the permission to share it.
If you are author or own the copyright of this book, please report to us by using this DMCA report form. Report DMCA. Home current Explore. Words: Pages: Therefore, isolation of alkaloids from alkaloid-bearing plants necessitates the following: a Separation of the alkaloids from the non-alkaloidal materials. Dissolution in an Organic Solvent followed by an acid-base shake up.
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