The quality control, in-process control and stability testing of herbal medicinal
products is performed by the use of characteristic markers as reference standards.
The content of these reference standards is usually assigned indirectly by the combination
of two chromatographic methods, water content by Karl Fischer and determination of
residue solvents and of inorganic impurities. However, this procedure is not very
accurate if the purity of the material is below 99.5%. As these marker substances
are usually isolated from plants it is very difficult to achieve the needed high purity
like 99.5% with a reasonable effort. Employment of quantitative NMR (qNMR) spectroscopy
as a relative primary method increases the reliability of the content assignment of
reference standards and their qualification [1]. The basis of qNMR is the direct proportionality
of the signal intensity with the number of protons contributing to the resonance line
[2, 3]. The marker compound is evaluated against an internal standard which is weighed
together with the marker compound into an NMR tube. The application of qNMR for the
content assignment of herbal markers was comprehensively validated within a public-funded
project [4]. This technique was applied for the content assignment of a series of
substances with relevance for the use as reference standards for herbal medicinal
products. Results will be presented for different markers and the chances and limitations
of this way of content assignment will be discussed.
Fig.1
References: 1. Veit, M.; Wissel, S. pharmind 2008, 1, 135–138.
2. Malz, F.; Jancke, H.: Validation of quantitative NMR. Journal of Pharmaceutical
and Biomedical Analysis 2005, 38, 813–823.
3. Jancke, H. NMR als primäre Methode. Nachrichten aus Chemie, Technik und Laboratorium,
1998, 46 722.
4. Malz, F.; Jancke, H. Validation of quantitative NMR. Journal of Pharmaceutical
and Biomedical Analysis 2005, 38, 813–823.
