Qualitative and Quantitative Analysis of Herbal Medicines

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.