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DOI: 10.1055/s-0030-1264829
Quantitative NMR: A useful tool for the content assignment of reference standards for quality control of herbal medicinal products
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.
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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.