High-Performance Liquid Chromatography--A Useful Tool for Determining Active Constituents and Adulterants in Traditional Chinese Herbal Medicines


Today, alternative therapies including traditional Chinese herbal medicines (TCHM) have achieved astonishing popularity even though they are not encouraged by the U.S. Food and Drug Administration, which classifies most plant drugs as dietary supplements or food additives and also places severe limitations on labelling. Also, unlike conventional drugs, TCHM are not regulated for their purity or potency. So, with the persistent trend of this latest green revolution, health care authorities around the world have found it a daunting task to promote the standardization of TCHM. There are many reasons for this.

Firstly, many active constituents of TCHM are thought to function synergistically in the system to achieve the desired effect. Hence, the standardization of only a single constituent may not be the best way to deliver consistent health results. Secondly, the standardization process should really begin with the growers/suppliers of raw materials. But regulations at this level are difficult to control and are influenced by biological and cultural factors. Thirdly, unlike synthetic drugs, pharmacological and toxicological knowledge about the specified chemical constituents of TCHM is patchy at best. And finally, there is still no general agreement regarding the precise analytical methods that should be used in the monographs or Pharmacopoeia to identify known chemicals.

Where HPLC Tools Come In

Despite the drawbacks, chemical analysis of active constituents--as well as of adulterants--present in TCHM is necessary to ensure quality control and consumer safety. As a result, the employment of qualitative or quantitative chromatographic techniques such as high-performance liquid chromatography (HPLC) could be very useful for quality control of TCHM.

HPLC emerged as a powerful analytical tool during the 1970s as progress was made in bonding durable phases to silica. To date, HPLC has advanced to be the analytical separation method of choice for clinical, forensic, and pharmaceutical fields. As in the pharmaceutical industry, HPLC could be regarded as the central standardization workhorse in many TCHM analytical or manufacturing laboratories. Nowadays, HPLC equipment is very sophisticated and reliable, and it comes with different types of detector and autosamplers as well as computers that control operation, processing, data storage, and retrieval.

Increasingly, HPLC analytical techniques have been included in many of the latest monographs on the identification and determination of the plant constituents as well as the adulterants in TCHM. Although there are limitations for these techniques, using HPLC avoids the main problems associated with the use of gas chromatography such as thermal stability of components, their high molecular mass, compound destruction, and polarity of the compound.

Acquiring and Honing HPLC Skills

If you want to become a competent HPLC analyst, you?ll need to acquire hands-on knowledge of the operation, maintenance, trouble-shooting, and data processing of HPLC. Only then can you use the system as a reproducible and reliable analytical tool. Such skills are best acquired through graduate training in analytical chemistry and allied fields and honed through practice and continual learning and upgrading.

Personally, my suggestion for upgrading these skills is through annual attendance of comprehensive training workshops/courses that are organized by corporations such as the HPLC manufacturer and specialist, Waters Corp.. Waters Corp. offers training courses that include basic to advanced material for all analysts, and its Connection University provides a cutting-edge curriculum, hands-on lab training, and experienced, certified instructors dedicated to providing knowledge and skills for chromatographers.

In addition, you need to stay relevant and current by keeping abreast of the latest know-how and technology relevant to the analysis of TCHM. You can best do that by staying on top of the pertinent scientific journals (e.g., The Journal of Chromatography B ), reading specific reference books, and visiting HPLC manufacturers? Web sites (e.g., Waters Corp. or Agilent Technologies).

Regular upgrading and understanding of the newest HPLC column and detector technologies are of paramount importance, but identifying and using better software cannot be overlooked.

HPLC as a TCHM Analytical Tool

The versatility of HPLC in compound separation is due mainly to the availability of numerous chromatographic matrices (reversed-phase, normal phase, ion-exchange, ion-pair, and others), its reproducibility (peak performance and results), and its selectivity (compounds of specific moieties/structures). The most popular matrix for herbal products analysis is reversed-phase column, a silica-based matrix to which a hydrocarbon chain of specified length is chemically bonded. These columns separate the analytes on the basis of their hydrophobic interactions with the bonded reversed-phase (stationary phase).

The various detectors, such as photodiode-array detectors (PDA), fluorescence detectors, electrochemical detectors, and mass-spectrometers, that are used to identify and quantify column throughputs have only enhanced the power of HPLC in the quality control and standardization of natural products. Ultraviolet detectors are the primary means of detection in the HPLC analysis of alkaloids and adulterants. Fixed wavelength (254 and/or 280 nm) and multiwavelength detectors like PDA have been widely employed with sensitivity in the nanogram range or even lower. HPLC-MS has revolutionised the study of plant alkaloids as it also provides information on the possible structure and molecular weight of the parent alkaloid or its metabolites.

For batch-to-batch reproducibility, HPLC identification tests are required to confirm the presence of the active constituents and potential adulterants in the TCHM. Although the quantification of the individual active constituents of TCHM is difficult, the use of HPLC-PDA has enabled analytical quality control of some herbal preparations. This technique can generate chemical spectra profile that characterizes the multicomponents of active constituents as uniquely as a fingerprint. A ?fingerprint chromatogram? covering a broad range of constituents may be stored electronically and its basic pattern/profile (as reference standard) can be used for comparison with a given test sample to determine a ?match factor.? This technique can define the identity of active plant constituents with greater accuracy than the conventional practice of measuring selected main constituents.

HPLC is also used to identify adulterants present in TCHM. Such adulterants may be formed or introduced during harvesting, drying, storing, and manufacturing processes. And the deliberate adulteration of TCHM materials is not infrequent. Typical adulterants include heavy metals, toxic alkaloids, pesticides/herbicides, mycotoxins, and others. Because carcinogenic mycotoxins such as ochratoxin A or aflatoxins are usually present or formed in agricultural commodities such as herbal/plant materials that are kept under hot and humid conditions, their analyses in TCHM are important.

Increasing Demand for HPLC Analysts in TCHM Sector

The drive for standardization of TCHM in Asia is significant, especially after China (the World?s largest TCHM exporter) entered the World Trade Organisation. In order for Asia to claim the place on the world stage that it feels it deserves, more emphasis on Good Manufacturing Practices requirements in line with international standards are necessary. Inevitably, this trend will demand more HPLC analysts to be trained for the TCHM sector.

Analysts/chemists in TCHM R&D laboratories and TCHM manufacturing industries who are involved in extraction and formulation of herbal products need to upgrade their skills on HPLC for batch-to-batch identification and standardization protocols. The same also applies to those working to regulate TCHM production and to those in private commercial laboratories who require HPLC skills or knowledge to check and control the purity or efficacy of the TCHM.

As mentioned above, deliberate adulterations of TCHM with Western medicines (including steroids, antibiotics, anti-inflammatory drugs, and diuretics) to increase potency have occurred. Recently, in Singapore, a TCHM slimming product called ?Slim 10? was adulterated with fenfluramine and phentermine (fen-phen), causing one death and severe liver damage in 14 others. The incidents prompted the Ministry of Health of Singapore to recommend (1) enforcement activities on Chinese proprietary medicines (CPM), (2) establishing a CPM Advisory Committee to evaluate and grant licences on CPM products to manufacturers and importer/wholesalers, and (3) setting up a CPM Listing Unit to process applications for product listings or licensing. Undoubtedly, all these enforcements or implementation of CPM control would safeguard and improve the confidence of the public in CPM, as well as ?standardize and strengthen? the position of TCHM research and development (R&D) and TCHM industry in Singapore.

Currently, in Singapore, as with the rest of Asia, there is a shortage of well-trained HPLC analysts in TCHM R&D laboratories and TCHM manufacturing industries. Some regional governments such as in Hong Kong and Singapore are actively trying to address these shortcomings by increasing spending on training and courses such as analytical chemistry. However, this innovation road on TCHM is going to be a slow and gruelling one because the cultural mindset changes for Asians (both practitioners and consumers) on their traditional practice (i.e., manufacturing and usage) of herbal medicines are not easy.

Nevertheless, HPLC, with its advanced, reliable column- and detector-technologies, will remain the central analytical tool for pharmaceutical and TCHM industries for a long time to come, and scientists competent in this analytical tool will continue to be sought after as Asia modernizes and upgrades its TCHM industries.

Suggested Further Reading

Official Methods of Analysis of the Association of Official Analytical Chemists (AOAC), Kenneth Helrich (Ed.), 15th Edition (AOAC Inc., Virginia, 1990).

World Health Organisation monographs on selected medicinal plants, Vol. 1 (WHO, Geneva, 1999).

Herbal Drugs and Phytopharmaceuticals, Norman Grainger Bisset (Ed.), English Edition (CRC Press, Boca Raton, 1994).

Follow Science Careers

Search Jobs

Enter keywords, locations or job types to start searching for your new science career.

Top articles in Careers