Medicinal Plants Classification Biosynthesis and ... - Index of

Non-Invasive Near Infrared Spectroscopic Techniques for the Characterization...
2. Near Infrared Spectroscopy
In near infrared spectroscopy (NIRS) excitation of molecules is accomplished in a
wavelength range between 750 and 2500 nm, corresponding to a wavenumber range between
4000 and 12.800 cm -1 [13, 14]. In the infrared region molecules containing C-H, C-O, C=O,
N-H and O-H functional groups are excited to stretching-, deformation- and scissorvibrations,
which overtones and combinations can be found in the near infrared region [15].
Spectra are recorded by light interaction with the material of interest and reflection of a part
of the reflected light to a PbS-detector, which transforms the optical signal into an
electronical. Differences in spectra are very often marginal so that a visual interpretation of
overlapping vibration bands is in many cases in praxis impossible. Chemometrics, a
mathematical, statistical, multivariate tool is applied for further treatment of recorded spectra
(Figure 1).
Principle of NIR Measurements
Figure 1. Principle of near infrared spectroscopy (NIRS)
The established, optimised and validated mathematical calibration model can then be
used in order to determine the presence and /or the concentration of a certain component [16-
18].
The main advantages of the near infrared spectroscopic (NIRS) method for the
characterisation of medicinal plants and their components are:
Short analysis time of only a few seconds enabling high sample throughput
Non invasive
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