Fourier transform infrared spectroscopy as a non-destructive method for analysing herbarium specimens

Abstract

Dried plant specimens stored in herbaria are an untapped treasure chest of information on environmental conditions, plant evolution and change over many hundreds of years. Owing to their delicate nature and irreplaceability, there is limited access for analysis to these sensitive samples, particularly where chemical data are obtained using destructive techniques. Fourier transform infrared (FTIR) spectroscopy is a chemical analysis technique which can be applied non-destructively to understand chemical bonding information and, therefore, functional groups within the sample. This provides the potential for understanding geographical, spatial and species-specific variation in plant biochemistry. Here, we demonstrate the use of mid-FTIR microspectroscopy for the chemical analysis of Drosera rotundifolia herbarium specimens, which were collected 100 years apart from different locations. Principal component and hierarchical clustering analysis enabled differentiation between three main regions on the plant (lamina, tentacle stalk and tentacle head), and between the different specimens. Lipids and protein spectral regions were particularly sensitive differentiators of plant tissues. Differences between the different sets of specimens were smaller. This study demonstrates that relevant information can be extracted from herbarium specimens using FTIR, with little impact on the specimens. FTIR, therefore, has the potential to be a powerful tool to unlock historic information within herbaria.

From Dormant Collections to Repositories for the Study of Habitat Changes: The Importance of Herbaria in Modern Life Sciences

“…Interestingly, several digitization projects also made old and ancient figurative herbaria available, which reported data about the discovery, description, and distribution of each painted plant species; therefore, the availability of data on plant biodiversity from the 16th century actually indicates the anticipation of the advent of modern herbaria [17,18]. The availability of large collections of herbarium specimens also favors analyses with imaging techniques involving newly developed methods for spectral analyses [19,20]. For instance, a reflectance spectrum across a range of wavelengths may be used to perform measurements of the chemical and structural composition of plants, whereas patterns in an ultraviolet spectrum, as perceived by pollinators, can be used as a diagnostic character to distinguish morphologically similar species [19,21].…”

“…The availability of large collections of herbarium specimens also favors analyses with imaging techniques involving newly developed methods for spectral analyses [19,20]. For instance, a reflectance spectrum across a range of wavelengths may be used to perform measurements of the chemical and structural composition of plants, whereas patterns in an ultraviolet spectrum, as perceived by pollinators, can be used as a diagnostic character to distinguish morphologically similar species [19,21].…”

Advancing herbal medicine: enhancing product quality and safety through robust quality control practices

“…It is often employed to verify the presence of specific markers or active compounds in herbal raw materials ( Vestal, 1984 ; Hussain et al, 2015 ; Sontag et al, 2019 ). Fourier transform infrared spectroscopy (FTIR) is used to identify functional groups in raw materials, helping to assess their chemical composition ( Agustika et al, 2022 ; Barnes et al, 2023 ). Atomic absorption spectroscopy (AAS) is employed to detect and quantify the presence of heavy metals in raw materials, ensuring they are within safe limits ( Qu et al, 2016 ; Ortegón et al, 2022 ).…”

Differentiation of species and provenance of palm leaf manuscripts using Fourier-Transform infrared spectrocopy and chemometrics

“…Although a stable and direct contact with the analysed object is necessary, this non-invasive method has proven to be a valuable tool in the analysis of organic material e.g. herbarium specimens (Barnes et al 2023), cellulosic and textile fibres (Garside and Wyeth 2003;Peets et al 2019), painting canvases (M. Manfredi et al 2015), colourants (Marcello Manfredi et al 2017) and palm leaf manuscripts (Yu, Zhang, and Song 2023;Sharma, Singh, and Dighe 2018). Most research on palm leaf manuscripts, however, focused primarily on processing, writing methods or ink analysis (Yu, Zhang, and Song 2023) and a comprehensive analysis of FTIR spectra of palm leaves as analytical fingerprints has not yet been performed.…”