Apparent penetration depth in attenuated total reflection Fourier-transform infrared (ATR-FTIR) spectroscopy of Allium cepa L. epidermis and cuticle

Author(s)
Alexander Götz, Ramin Nikzad-Langerodi, Yannick Städler, Anke Bellaire, Johannes Saukel
Abstract

Over the past decades, ATR-FTIR has emerged as promising tool for the identification of plants at the genus and (sub-) species level through surface measurements of intact leaves. Theoretical considerations regarding the penetration depth of the evanescent wave into the sample and the thickness of plant leaf cuticles suggest that the structure and composition of the cuticle represent universal taxonomic markers. However, experimental evidence for this hypothesis is scarce. In the current contribution, we present results of a series of simple experiments on epidermal monolayers derived from the bulbs of Allium cepa L. (Amaryllidaceae) as a model system to study the effect of an IR active probe located beyond the theoretical penetration depth of the evanescent wave. We found that this probe had a significant influence on the ATR-FTIR spectra for up to 4 epidermal layers stacked on top of each other corresponding to a total thickness of around 60 μm, exceeding the theoretical penetration depth of the evanescent wave by a factor of around 20. Altogether, our data indicate a major discrepancy between theory and practice in ATR-FTIR spectroscopy in general and provide strong evidence that in general plant leaf spectra cannot be fully explained by the structure and composition of the cuticle alone.

Organisation(s)
Department of Botany and Biodiversity Research, Functional and Evolutionary Ecology
External organisation(s)
Universität Wien, Research Center for Non Destructive Testing (RECENDT)
Journal
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy
Volume
224
No. of pages
6
ISSN
1386-1425
DOI
https://doi.org/10.1016/j.saa.2019.117460
Publication date
01-2020
Peer reviewed
Yes
Austrian Fields of Science 2012
106008 Botany, 106012 Evolutionary research, 106042 Systematic botany
Keywords
ASJC Scopus subject areas
Analytical Chemistry, Instrumentation, Atomic and Molecular Physics, and Optics, Spectroscopy
Portal url
https://ucris.univie.ac.at/portal/en/publications/apparent-penetration-depth-in-attenuated-total-reflection-fouriertransform-infrared-atrftir-spectroscopy-of-allium-cepa-l-epidermis-and-cuticle(69127d3d-61bf-4d66-9291-96a119a646b5).html