Ebook Quality control of herbal medicines
The traditional herbal medicines (HM) and their preparations have been widely used for thousands of years in many oriental countries, such as in China, Korea, Japan, etc. How ever, one of the characteristics of oriental herbal medicine preparations is that all the herbal medicines, either presenting as single herbs or as collections of herbs in composite formulae, are extracted with boiling water during the decoction process. This may be the main reason why quality control of oriental herbal drugs is more difficult than that of western drug. As pointed in “General Guidelines for Methodologies on Research and Evaluation of Traditional Medicines (World Health Organization, 2000)”, “Despite its existence and continued use over many centuries, and its popularity and extensive use during the last decade, traditional medicine has not been officially recognized in most countries. Consequently, education, training and research in this area have not been accorded due attention and support. The quantity and quality of the safety and efficacy data on traditional medicine are far from sufficient to meet the criteria needed to support its use world-wide. The reasons for the lack of research data are due to not only to health care policies, but also to a lack of adequate or accepted research methodology for evaluating traditional medicine”.
In general, one or two markers or pharmacologically active components in herbs and or herbal mixtures were currently employed for evaluating the quality and authenticity of herbal medicines, in the identification of the single herb or HM preparations, and in assessing the quantitative herbal composition of an herbal product. This kind of the determination, however, does not give a complete picture of a herbal product, because multiple constituents are usually responsible for its therapeutic effects. These multiple constituents may work ‘synergistically’ and could hardly be separated into active parts. Moreover, the chemical constituents in component herbs in the HM products may vary depending on harvest seasons, plant origins, drying processes and other factors. Thus, it seems to be necessary to determine most of the phytochemical constituents 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 . Thus, several chromatographic techniques, such as high-performance liquid chromatography (HPLC), gas chromatography (GC), capillary electrophoresis (CE) and thin layer chromatography (TLC), can be applied for this kind of documentation. In this way, the full herbal product could 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 a herbal product should be constructed and compared with the profile of a clinically proven reference product.
In 2004, the Chinese State Food and Drug Administration (SFDA) will regulate the compositions of liquid injection with HM ingredients using stringent quality procedures such as chemical assay and standardization. Fingerprints of HM liquid injections are compulsorily carried out for this purpose. In addition, among the various experimental techniques, chromatographic methods are highly recommended for finding out the fingerprints of these products .
By definition, a chromatographic fingerprint of a HM is, in practice, a chromatographic pattern of the extract of some common chemical components of pharmacologically active and or chemically characteristics . This chromatographic profile should be featured by the fundamental attributions of “integrity” and “fuzziness” or “sameness” and “differences” so as to chemically represent the HM investigated . It is suggested that with the help of chromatographic fingerprints obtained, the authentication and identification of herbal medicines can be accurately conducted (“integrity”) even if the amount and/or concentration of the chemically characteristic constituents are not exactly the same for different samples of this HM (hence, “fuzziness”) or, the chromatographic fingerprints could demonstrate both the “sameness” and “differences” between various samples successfully . Thus, we should globally consider multiple constituents in the HM extracts, and not individually consider only one and/or two marker components for evaluating the quality of the HM products.
However, in any HM and its extract, there are hundreds of unknown components and many of them are in low amount. Moreover, there usually exists variability within the same herbal materials . Consequently, to obtain reliable chromatographic fingerprints that represent pharmacologically active and chemically characteristic components is not an easy or trivial work. Fortunately, chromatography offers very powerful separation ability, such that the complex chemical components in HM extracts can be separated into many relatively simple sub fractions. Furthermore, the recent approaches of applying hyphenated chromatography and spectrometry such as high-performance liquid chromatography diode array detection (HPLC–DAD),gas chromatography mass spectroscopy (GC–MS), capillary electrophoresis-diode array detection (CE-DAD), HPLC–MS and HPLC–NMR, could provide the additional spectral information, which will be very helpful for the qualitative analysis and even for the 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 . If hyphenated chromatography is further combined with chemometric approaches, clear pictures might be developed for chromatographic fingerprints obtained. These excellent properties are the so-called dimension advantages proposed by Booksh and Kowalski . A chemical fingerprint obtained by hyphenated chromatography, out of question, will become the primary tool for quality control of herbal medicines .
Contents
1. Introduction
2. Chromatography and chemical fingerprints of herbal medicines
- 2.1. Thin layer chromatography
2.2. Gas chromatography and volatile components in herbal medicines
2.3. High-performance liquid chromatography
2.4. Electrophoretic methods
3. Hyphenation procedures
- 3.1. GC–MS and herbal medicines
3.2. HPLC–DAD, HPLC–MS and others
3.3. Hyphenation of CE
4. Information features of chromatographic fingerprints of herbal medicines
- 4.1. Phytoequivalence and chromatographic fingerprints of herbal medicines
4.2. Information contents of fingerprints of herbal medicines
4.3. Correction of retention time shift of fingerprints of herbal medicines
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