Read this article to learn about qualitative and quantitative analysis of herbal medicines.
For qualitative and quantitative analysis of phytochemicals, chromatography can be used. In general, one or two markers, or pharmacologically active components, in herbs are currently employed for evaluating the quality and authenticity of herbs or herbal extractions, for the identification of a single herb or herbal medicine preparation, and for assessing the quantitative herbal composition of an herbal formulated product.
This kind of determination, however, does not give a complete picture of an herbal product, because multiple constituents are usually responsible for its therapeutic effects. These multiple constituents may work synergistically and not all are necessarily present in the extract.
Moreover, the chemical constituents in component herbs in the herbal medicines may vary depending on harvest seasons, plant origins, drying processes and other factors.
Thus, it seems to be necessary to determine most of the phytochemicals of herbal products in order to ensure the reliability and repeatability of pharmacological and clinical research, to understand their bioactivities, and possible side effects of active compounds, and to enhance product quality control.
In recent years, significant efforts have been made to devise methods for the quality control of herbal materials as well as herbal preparations by utilizing quantitative methods and/or qualitative fingerprinting technologies. Both methods have advantages and disadvantages.
Quantitative analysis aims to separate and identify the marker compounds from herbs or herbal preparations and then use them as indicators, or standards, to assess quality. Determining the effective or principal chemical constituents and the toxic compounds is crucial to the quality control of herbs and herbal preparations.
Much attention has been drawn to the development of chromatographic methods in this field, and a great number of such papers have been published.
But for quality control of complex systems, the determination of only a few compounds cannot give a comprehensive and accurate assessment of all active constituents in herbal medicinal products. This approach is therefore inherently inadequate for quality control and stability evaluation of herbal medicinal products.
Several chromatographic techniques, such as HPLC, GC, CE and TLC, can be applied for this kind of documentation. In this way, the full herbal product can be regarded as the active ‘compound’. The concept of phytoequivalence was developed in Germany in order to ensure consistency of herbal products.
According to this concept, a chemical profile, such as a chromatographic fingerprint, for an herbal product should be constructed and compared with the profile of a clinically proven reference product.
By definition, a chromatographic fingerprint of an herbal product is, in practice, a chromatographic pattern of the extract of some common chemical components of pharmacologically active and/or chemical characteristic.
This chromatographic profile should be featured by the fundamental attributions of “sameness” and “differences” so as to chemically represent the herbal product investigated.
It is suggested that with the help of chromatographic fingerprints obtained, the authentication and identification of herbal medicines can be accurately conducted (“sameness“), even if the amount and/ or concentration of the chemical characteristic constituents are not exactly the same for different samples of this herbal preparation (hence, “differences“).
We should globally consider multiple constituents in the herbal product extracts, and not consider only one and/or two marker components for evaluating the quality of the herbal products.
In any herbal product and its extract, there are hundreds of unknown components and many of them are in low amounts. Moreover, there usually exists variability within the same herbal material.
Consequently, to obtain reliable chromatographic fingerprints that represent pharmacologically active and chemical characteristic components is not an easy task. Fortunately, chromatography offers very powerful separation ability, such that the complex chemical components in herbal product extracts can be separated into many relatively simple sub-fractions.
Furthermore, the recent approaches of applying ‘hyphenated’ chromatography and spectrometry, such as HPLC- PDA, GC-MS, HPLC-MS and HPLC-NMR, could provide the additional spectral information which will be very helpful for the qualitative analysis, and even for on-line structural elucidation.
With the help of the spectral information the ‘hyphenated’ instruments show greatly improved performances in terms of the elimination of instrumental interferences, retention time shift correction, selectivity, chromatographic separation abilities, measurement precision.
A chemical fingerprint obtained by ‘hyphenated’ chromatography, will without question, remain the primary tool for quality control of herbal medicines for many decades.