In the official pharmacopoeia there are general methods of evaluation, both chemical and biological. However, pharmacognosy also uses much more sophisticated methods, such as spectroscopic and chromatographic methods.
The evaluation of the quality of the drugs from the chemical point of view provides a marked in-depth analysis, peculiar to the analytical capacity of the instruments used; in other words, a drug is evaluated on the basis of the quantity and quality of the active principles contained in it, which are determinant in an analytically precise way thanks to extremely precise chromatographic instruments. Among these chromatographic techniques we find: gas chromatography, mass gas, HPLC (liquid chromatography on column), ion-exchange chromatography and plate chromatography (TLC, HPTLC). These are all methodologies that use the chromatographic principle in the qualitative-quantitative evaluation of the chemical substances present in a phytocomplex. Therefore, these instruments allow us to evaluate the drug as a phytocomplex, the quantity and quality of the individual chemical classes, their ratio and the quantity of the characterizing active principle.
To evaluate the phytocomplex it is important to adopt the most suitable strategies for its extraction, because there is no analytical method that has not been preceded by an extraction. The extractions are necessary for the technical-pharmacognostation to evaluate the drug or, possibly, to obtain elements of use of this drug, which can be directly placed in the tertiary sector. Extraction methods make it possible to obtain those categories of active principles that are considered important in the qualitative classification of the drug, or to selectively extract one or more categories that are considered an expression of its activity.
The active principles, generally, are molecules of glycosides, alkaloids, terpenes, anthraquinones; all secondary metabolites that are expression of the relational biology of the organism; there are, however, also molecules deriving from the primary metabolism of health interest, such as carbohydrates (starch and its derivatives, cellulose and its derivatives), proteins and in particular proteolytic enzymes (papain or bromelain).
Before proceeding with an extraction of active principles from a drug, it is necessary to consider the chemical-physical characterization of the latter; in other words, before extracting an active ingredient it is necessary to know well its chemical nature in terms of polarity, because the extraction process is essentially reduced to the association of a suitable solvent with the drug. This solvent, being chemically akin to the principle to be extracted, selectively removes it from the remaining phytocomplex; the more this chemical affinity is accentuated, the better the extraction will take place ("the like dissolves the like"). It is therefore essential to know, from the phytochemical point of view, the principle to be extracted, in order to associate the solvent or the solvent mixture more similar to it.
