Chemical nature of herbal drugs constituents can be used as tool to device a method for the analysis of the constituents. It involves:
- chemical tests
- chemical assay
- and also the phytochemical investigation of the crude drugs.
Types of Chemical Tests for Herbal Drugs Evaluation
Some important chemical tests used in chemical analysis are:
- Dragendorff’s test for alkaloids gives a yellow orange precipitate
- Molisch’s tests for carbohydrates gives a purple to violet colour rings
- Ferric chloride test for tannins gives a blue colour etc.
The chemical tests are used for the determination of specific chemical constituents which may be present in any drug to which its therapeutic activity is attributed.
Other Types of Herbal Drugs Chemical Evaluation Method
Chemical evaluation methods also involves the use of:
- Chromatographic Method
- Spectroscopic Methods
Use of this sophisticated instruments to achieve standardisation has various benefits some of which are: This covers screening, isolation, identification and purification of the chemical components. Chemical analysis of the drug is done to assess the potency of vegetable material in terms of its active principles.
1. Chromatography
Chromatography is the science which studies the separation of molecules based on differences in their structure and/or composition.
In general, chromatography involves moving a preparation of the materials to be separated, “the “test preparation”, over a stationary support. The molecules in the test preparation will have different interactions with the stationary support leading to separation of similar molecules.
Test molecules which display tighter interactions with the support will tend to move more slowly through the support than those molecules with weaker interactions. In this way, different types of molecules can be separated from each other as they move over the support material.
Chromatographic separations can be carried out using a variety of supports, including immobilized silica on glass plates (thin layer chromatography), very sensitive High Performance Thin Layer Chromatography (HPTLC), volatile gases (gas chromatography), paper (paper chromatography), and liquids which may incorporate hydrophilic, insoluble molecules (liquid chromatography).
High performance thin layer chromatography (HPTLC) is a valuable quality assessment tool for the evaluation of botanical materials. It allows for the analysis of a broad number of compounds both efficiently and cost effectively. Additionally, numerous samples can be run in a single analysis thereby dramatically reducing analytical time. With HPTLC, the same analysis can be viewed collectively in different wavelengths of light thereby providing a more complete profile of the plant than is typically observed with more specific type of analysis.
2. Spectroscopic Methods
There are several spectroscopic techniques which can be used to identify organic molecules: infrared (IR), mass spectroscopy (MS) UV/visible spectroscopy (UV/Vis) and nuclear magnetic resonance (NMR).
IR, NMR and UV/vis spectroscopy are based on observing the frequencies of electromagnetic radiation absorbed and emitted by molecules.
MS is based on measuring the mass of the molecule and any fragments of the molecule which may be produced in the MS instrument. This MS spectrum gives information about the molecule mass, molecular formula and qualitative determination of a known compound.