19 Bio-applications of NIR Spectroscopy
415
of sampling conditions. Worth mentioning is a relatively well-established functional
NIR spectroscopy in medical diagnosis, where it serves the purpose of functional
neuroimaging.
19.2 Medicinal Plant Analysis
Most often, the therapeutic and medicinal properties of herbs and plants are related
to individual bio-active compounds, and their content affects the general usefulness
of a given natural product. The chemical composition and the concentration of the
bio-active compounds can be analyzed by NIR spectroscopy. The worldwide trend
in using medicinal plant products is permanently increasing. In 2018, the turnover
with freely available products from pharmacies was more than 1 billion Euro and that
from other sources including online business more than another 1 billion Euro. This
trend creates high demand for high throughput, in situ analytical methods capable
of fast, non-invasive, simultaneous analysis of chemical and physical parameters in
order to ensure quality of the natural medicine. Analytical methodologies based on
portable, miniaturized NIR instrumentation are essentially favored for this purpose,
as direct assessment and optimization of the cultivation conditions and parameters
become possible, e.g., the harvest time. However, this application field remains quite
new, and the applicability and performance profiles of handheld NIR devices remain
continuously investigated.
Kirchler et al. described in their comprehensive examination the capability of NIR
spectroscopy supported with various tools to determine the antioxidative potential
and related properties of plant medicine. This trend-setting study proposed a new
analytical strategy [3]. The performances of one benchtop and two different types of
miniaturized NIR spectrometers were tested and compared for the first time by the
determination of the rosmarinic acid (RA) content of dried and powdered Rosmarinus
officinalis, folium (i.e., Rosmarini folium). The recorded NIR spectra (Fig. 19.1) were
utilized in hyphenation with multivariate data analysis (MVA) to calculate partial
least squares regression (PLSR) models (Table 19.1). Quality parameters obtained
from cross-validation (CV) revealed that the benchtop spectrometer achieved the
best result with a R
2 of 0.91 and a RPD of 3.27. Miniaturized NIR spectrometer
MicroNIR 2200 showed a satisfying calibration value R
2 of 0.84 and a RPD of 2.46.
The analysis performed by miniaturized microPHAZIR, with a R
2 of 0.73 and a RPD
of 1.88, was less precise and revealed room for improvements. All recorded spectra
of the different devices were additionally studied by two-dimensional correlation
spectroscopy (2D-COS; details on this technique are available in Chapter 6 Twodimensional correlation spectroscopy) analysis; in order to support the performed
PLS regression models (Fig. 19.2). Differences in the sensitivity of the spectrometers
were visualized by 2D hetero-correlation plots as well. These approaches were found
to be helpful to identify discrepancies between microPHAZIR and MicroNIR 2200
compared to the benchtop instrument. With the aim to obtain a better understanding
of the factors which determine the analyzed PLS regression models, in this study,
415
of sampling conditions. Worth mentioning is a relatively well-established functional
NIR spectroscopy in medical diagnosis, where it serves the purpose of functional
neuroimaging.
19.2 Medicinal Plant Analysis
Most often, the therapeutic and medicinal properties of herbs and plants are related
to individual bio-active compounds, and their content affects the general usefulness
of a given natural product. The chemical composition and the concentration of the
bio-active compounds can be analyzed by NIR spectroscopy. The worldwide trend
in using medicinal plant products is permanently increasing. In 2018, the turnover
with freely available products from pharmacies was more than 1 billion Euro and that
from other sources including online business more than another 1 billion Euro. This
trend creates high demand for high throughput, in situ analytical methods capable
of fast, non-invasive, simultaneous analysis of chemical and physical parameters in
order to ensure quality of the natural medicine. Analytical methodologies based on
portable, miniaturized NIR instrumentation are essentially favored for this purpose,
as direct assessment and optimization of the cultivation conditions and parameters
become possible, e.g., the harvest time. However, this application field remains quite
new, and the applicability and performance profiles of handheld NIR devices remain
continuously investigated.
Kirchler et al. described in their comprehensive examination the capability of NIR
spectroscopy supported with various tools to determine the antioxidative potential
and related properties of plant medicine. This trend-setting study proposed a new
analytical strategy [3]. The performances of one benchtop and two different types of
miniaturized NIR spectrometers were tested and compared for the first time by the
determination of the rosmarinic acid (RA) content of dried and powdered Rosmarinus
officinalis, folium (i.e., Rosmarini folium). The recorded NIR spectra (Fig. 19.1) were
utilized in hyphenation with multivariate data analysis (MVA) to calculate partial
least squares regression (PLSR) models (Table 19.1). Quality parameters obtained
from cross-validation (CV) revealed that the benchtop spectrometer achieved the
best result with a R
2 of 0.91 and a RPD of 3.27. Miniaturized NIR spectrometer
MicroNIR 2200 showed a satisfying calibration value R
2 of 0.84 and a RPD of 2.46.
The analysis performed by miniaturized microPHAZIR, with a R
2 of 0.73 and a RPD
of 1.88, was less precise and revealed room for improvements. All recorded spectra
of the different devices were additionally studied by two-dimensional correlation
spectroscopy (2D-COS; details on this technique are available in Chapter 6 Twodimensional correlation spectroscopy) analysis; in order to support the performed
PLS regression models (Fig. 19.2). Differences in the sensitivity of the spectrometers
were visualized by 2D hetero-correlation plots as well. These approaches were found
to be helpful to identify discrepancies between microPHAZIR and MicroNIR 2200
compared to the benchtop instrument. With the aim to obtain a better understanding
of the factors which determine the analyzed PLS regression models, in this study,