Advances of infrared spectroscopy in natural product research

Natural product's properties are related to certain classes of compounds such as alkaloids, flavonoids, essential oils and others. 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, qualitative and quantitative analysis of individual compounds. In food industry, spectroscopic investigations using infrared radiation have been used to monitor and evaluate the composition and quality already since the early sixties. During the last four decades near-infrared spectroscopy (NIR; 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 non-invasive analytical tool allowing a fast and simultaneous qualitative and quantitative characterization of natural products and their constituents. Additionally, the development of custom-made hand-held instruments enables infield measurement for determining the optimum harvest time. Attenuated total reflection (ATR) and Fourier transform infrared (FTIR) spectroscopic imaging are suitable not only for the differentiation of different plant species, but also to distinct various ingredients within a plant. FTIR spectroscopic microscopy enables molecular imaging of complex botanical samples and therefore the detection and characterization of the molecular components of biological tissue. In the present contribution, the principle, technique and methodology of the different infrared spectroscopic methods are described followed by a discussion of quantitative and qualitative application possibilities in the field of natural product analysis. (C) 2014 Phytochemical Society of Europe. Published by Elsevier B.V. All rights reserved.