|Author: ||H. Schulz|
|Keywords: ||ATR-IR spectroscopy, NIRS, NIR-FT Raman spectroscopy, quality control, secondary metabolites|
During the last years especially Near-Infrared Spectroscopy (NIRS) has been introduced as a very efficient and non-destructive analytical tool for the reliable de-termination of secondary metabolites in medicinal and aromatic plants.
In this con-text, feasibility studies were performed in order to get a deeper insight regarding possible applications, but limits of NIR spectroscopy were also pointed out in this special field of research.
Up to now, numerous NIR calibrations have been developed to predict simultaneously the amount of minor volatile as well as non-volatile sub-stances in various tea drugs, medicinal herbs and aromatic plants (e.g. Carum carvi, Foeniculum vulgare, Mentha x piperita, Salvia officinalis, Origanum marjorana, Thymus vulgaris, Chamomilla recutita, Papaver somniferum, Rosmarinus officinalis, Echinacea angustifolia, Echinacea pallida, Aspalathus linearis, Camellia sinensis). Since in principle NIRS measurements can also be performed on fresh plant material, it is possible to use this method for the prediction of the optimal har-vest time or for the selection of individual genotypes directly in the field.
Recently, a special mid-infrared technique (ATR/FT-IR) in combination with sophisticated chemometrical algorithms was also found to have some potential for direct plant analysis without the necessity to perform any clean-up procedures.
In contrast to NIR measurements, the observed fundamental absorption bands occurring in the mid-infrared (MIR) range can be related to concrete functional groups of the indi-vidual analyte molecules.
Furthermore, NIR-FT-Raman spectroscopy, which is to be seen as a complementary method to MIR, has already been applied to investigations of distinctive substances in several medicinal and aromatic plants.
Using Nd:YAG laser excitation at 1064 nm, various important plant substances were analysed non-destructively and the observed “key Raman bands” were discussed with regard to the corresponding pure standard components (e.g. polyacetylenes, gentiopicroside, curcumin, cinnamyl aldehyde).
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