Raman and IR Spectroscopic Methods for Determination of Valuable Plant Components
Hartwig Schulz
Federal Centre for Breeding Research on Cultivated Plants (BAZ), Institute for Plant Analysis,
Neuer Weg 22-23, D-06484 Quedlinburg, Germany. E-mail: H.Schulz@bafz.de.
In order to ensure the quality of drugs used as raw materials for the production of cosmetic materials
aroma extracts or phytopharmaceutical products, usually GC and HPLC combined with different
detection systems (e.g. FID, MS, UV-Vis, fluorescence) is applied. Since these methods are mostly
time-consuming and comparatively expensive, some attempts have been made to find alternative
analytical options. In this context several new vibrational spectroscopy methods in combination with
sophisticated chemometric algorithms were successfully introduced during recent years (e.g. using
NIR-, ATR-IR- and Raman spectroscopic techniques) for an efficient determination of the individual
essential oil components [1]. Whereas NIRS data can be interpreted only by application of statistical
methods, Raman spectra in most cases present characteristic key bands of the individual volatile
fraction and therefore in principle allow easily the discrimination of different plant species or
chemotypes. Raman spectroscopy has also proven to be a fast and reliable method for quality control
of various isolated extracts requiring both minimal sample preparation and minimum amount of
analyte. Furthermore, this technique principally allows to identify non-destructively various
components in fresh plant material if characteristic key bands of the individual analyte molecules can
be found in the spectrum [2,3]. In this context, especially NIR FT Raman spectroscopy has been
described as a valuable tool for in vivo investigations because fluorescence and thermal decomposition
of the plant tissue can be reduced to a minimum. Several examples present the special potential of
vibrational Raman microspectroscopy providing detailed information about microstructure and
chemical composition of the analysed plant material. Raman area mappings allow to obtain 2dimensional spectroscopic images of the investigated samples which can be directly compared to the
corresponding visual image. Furthermore, mapping provides detailed information regarding the
distribution of specific plant substances occurring in the surface layer [4-6]. Based on these data not
only qualitative but also semi-quantitative interpretation of the spectroscopic measurements is
possible. Contrary to IR imaging, Raman mapping does not need any sample preparation and can be
also performed at intact living plant material.
1.
H. Schulz (2004) Application in analysis of coffee, tea, cocoa, tobacco, spices, medicinal and aromatic
plants, and related products. In: Roberts, C.; Workman, J.; Reeves, J. (Eds.): Near-infrared Spectroscopy in
Agriculture, American Society of Agronomy - Crop Science of America - Soil Science Society of America,
Madison, USA, Agronomy Monograph, No. 44, 345-376
2.
H. Schulz, R. Quilitzsch, H. Krüger (2003) Rapid evaluation and quantitative analysis of thyme, origano and
chamomile essential oils by ATR-IR and NIR spectroscopy; J. Mol. Struct. 661-662, 299-306
3.
H. Schulz, M. Baranska, H.-H. Belz, P. Rösch, M. Strehle, J. Popp (2004) Chemotaxonomic characterisation
of essential oil plants by vibrational spectroscopy measurements, Vib. Spectrosc. 35, 81-86
4.
M. Baranska, H. Schulz, P. Rösch, M.A. Strehle, J. Popp (2004) Identification of secondary metabolites in
medicinal and spice plants by NIR-FT-Raman microscopic mapping,
Analyst 129, 926-930
5.
B. Schrader, H. Schulz, M. Baranska, G.N. Andreev, C. Lehner, J. Sawatzki (2004) Non-destructive Raman
analyses – Polyacetylenes in plants, Spectrochim. Acta (accepted for publication)
6.
H. Schulz, M. Baranska, R. Baranski (2004) Potential of NIR-FT-Raman spectroscopy in natural carotenoid
analysis; Biopolymers (accepted for publication)