Near‐Infrared Spectroscopy in Natural Product Research

Abstract

The properties of natural products are related to certain classes of compounds such as alkaloids, flavonoids, and essential oils. Traditionally, separation techniques including thin‐layer chromatography (TLC), liquid chromatography (LC), gas chromatography (GC), and capillary electrophoresis (CE) even hyphenated to mass spectrometry (MS) were used for the elucidation and qualitative and quantitative analyses of individual compounds. In the food industry, spectroscopic investigations using infrared radiation have been used to monitor and evaluate the composition and quality since the early 1960s. During the last four decades, near‐infrared (NIR) spectroscopy (800–2500 nm; 12,500–4000 cm −1 ) has become one of the most attractive and used methods for analysis for the following reasons: It represents a noninvasive analytical tool allowing a fast and simultaneous qualitative and quantitative characterization of natural products and their constituents. In this contribution, the principle, technique, and methodology are described followed by a discussion of quantitative and qualitative application possibilities. Finally, some hints to helpful regulatory issues and advantages and limitations are critically evaluated.

Breakthrough Potential in Near-Infrared Spectroscopy: Spectra Simulation. A Review of Recent Developments

“…Nowadays NIRS is being widely used in modern analytical applications due to a uniquely synergistic combination of qualities. Its universality, wide applicability, uncomplicated instrumentation, low time-to-result and low cost factors are prominent advantages from the point of view of qualitative and quantitative analysis (Ciurczak and Drennen, 2002; Siesler et al, 2002; Cozzolino, 2014; Huck, 2014, 2016a; Ozaki et al, 2017). It enables the non-invasive, non-destructible analysis of a variety of samples while maintaining a good balance between its cost, time, and analytical performance.…”

“…The mentioned typical low absorptivity in NIR (Figure 1) results in the ability of examining a bulk sample in high volume with no limitation to the sample surface, as often encountered in optical spectroscopy. NIRS has found its way to quality control laboratories dealing with, e.g., food (Smyth and Cozzolino, 2013; Henn et al, 2016; Ringsted et al, 2017; Chapman et al, 2018) and natural products (Pezzei et al, 2017a), agriculture-related items (Pezzei et al, 2017b), pharmaceuticals (Kirchler et al, 2017a; Yan and Siesler, 2018a), phytopharmaceuticals (Stecher et al, 2003) and phytoanalysis in general (Huck, 2017a), polymers (Huck, 2016b; Unger et al, 2016; Yan and Siesler, 2018b) fuel (Lutz et al, 2014a), cosmetics 2 (Blanco et al, 2007), biomedical applications (Jue and Masuda, 2013), general industry (Huck, 2017b) and environmental studies (Altinpinarn et al, 2013; Roberts and Cozzolino, 2016, 2017), among others (Ciurczak and Drennen, 2002; Siesler et al, 2002; Iwamoto, 2009; Cozzolino, 2014; Huck, 2014, 2016a; Ozaki et al, 2017; Power et al, 2018; Yan and Siesler, 2018c). In response to strong demand from the industry the instrumentation has been undergoing continuous development.…”

“…Basic NIR investigations of the chemical structure, molecular vibrations, and intra- and inter-molecular interactions remain limited in relation to the exceedingly active field of applied studies (Huck, 2014). Due to an intrinsic complexity of NIR spectra, reflecting the anharmonic nature of molecular vibrations (Huck, 2014; Ozaki et al, 2017) the observed spectral outline typically emerges from multiple overlapping contributions. The resulting broad and non-homogeneous bands create significant difficulties in the comprehensive association of the observed spectral variability and physicochemical background.…”

“…Bio-significant molecules remain near the center of attention of applied NIRS. Qualitative and quantitative analysis of natural products (e.g., raw biomaterials, intermediate and final products) is a strongly developing field of applications (Huck, 2014, 2016a); this fact focuses attention on biomolecules. NIRS in hyphenation with chemometrics (multivariate analysis; MVA) uses rich chemical information entangled in the NIR spectrum of complex samples and correlates it with the chosen property of sample (Ozaki et al, 2006).…”

“…Near-infrared spectroscopy (commonly abbreviated as NIRS) has distinguished itself by a remarkable evolution from an undervalued section of vibrational spectroscopy to one of the presently most widespread modern analytical techniques with strong prospects for further expansion (Ciurczak and Drennen, 2002; Siesler et al, 2002; Cozzolino, 2014; Huck, 2014, 2016a; Ozaki et al, 2017). The second major application field taking advantage of the potential embodied in NIRS is hyperspectral imaging (Ozaki et al, 2017; Türker-Kaya and Huck, 2017; Dorrepaal and Gowen, 2018; He et al, 2018), which enjoys a rapidly growing interest in the biomedical applications (He et al, 2015; Türker-Kaya and Huck, 2017) and is a subject of focused development nowadays (He et al, 2015; Sun et al, 2017; Wong et al, 2019).…”