Natural products have served mankind as a source of medicine since — and even before — historical records began. Herbal extracts
now play an important and growing role in disease prevention and therapy, and are used extensively as drugs and food additives.
Compared with synthetic chemical drug compounds, the composition of herbal extracts is far more complex. Consequently, their
quality control is becoming an increasingly important issue. For example, by the European legislation (directive 2004/24/EC
concerning "traditional herbal medicinal products") a more strict control on the quality and purity of these products is required.
This is also the case by the State Drug Administration of China. It involves, for example, the creation of a type of monograph
as a guideline to test the identity and quality.
Identity and quality can be derived from fingerprint chromatograms. These fingerprints can be defined as "a chromatographic
pattern of an herbal extract showing some common pharmacologically active and/or chemical characteristic compounds". An example
is shown in Figure 1. The entire fingerprints are used as a source of information because by assaying only a number of compounds
from the extract, the total intrinsic quality of the herb is not necessarily assessed.
Another reason for stricter quality control is to assess if other herbs/extracts are used than those expected. This can be
a result of conscious adulterations where another plant is sold, to the unconscious mistaken use of "look-alikes".
Confusion can also occur due to language. For example, when translating from Chinese pin-yin terminology into western languages
or when the same name is used in different regions for different parts of the plant, or even different species or genera.
An example of such a language confusion resulting in the mistaken use of a herb occurred in the beginning of the 1990s in
Belgium. Stephania tetrandra, which is used in a herbal treatment against obesity, was exchanged with Aristolochia fangchi, a herb resulting in a severe nephropathy because of the presence of aristolochic acid. Confusion probably occurred because
of the similarity in the pin-yin terminology of both plants: Feng Fangji vs. Guang Fangji, respectively.
The fingerprint chromatograms are also accepted by the World Health Organization (WHO) as an identification and qualification
technique for medicinal herbs. There are two main phases of a fingerprint approach:
- The development of the fingerprint.
- The extraction of information.
Analysis and handling of the fingerprint data is, therefore, an important aspect.
The main separation technique used in fingerprint development is high-performance liquid chromatography (HPLC) coupled to
ultraviolet (UV), electric light scattering (ELS) and, occasionally, mass spectrometry (MS) detection. For fingerprint development,
spectroscopic techniques, such as near infra-red (NIR), Raman, nuclear magnetic resonance spectroscopy (NMR), and other separation
techniques, including thin layer chromatography (TLC) and capillary electrophoresis (CE) can also be used.