Department of Pharmacognosy, University of Vienna, Vienna, Austria.
Department of Pharmacognosy, University of Vienna, Vienna, Austria; Research Center for Non Destructive Testing, RECENDT GmbH, Linz, Austria.
Spectrochim Acta A Mol Biomol Spectrosc. 2020 Jan 5;224:117460. doi: 10.1016/j.saa.2019.117460. Epub 2019 Aug 9.
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.
在过去的几十年中，ATR-FTIR 已成为一种有前途的工具，可通过对完整叶片进行表面测量来鉴定属和（亚）种水平的植物。关于消逝波进入样品的穿透深度和植物叶片角质层厚度的理论考虑表明，角质层的结构和组成代表通用的分类标记。但是，这种假设的实验证据很少。在本研究中，我们介绍了一系列简单实验的结果，这些实验是使用洋葱（百合科）鳞茎衍生的表皮单层作为模型系统进行的，以研究位于消逝波理论穿透深度之外的 IR 活性探针的影响。我们发现，对于彼此堆叠的多达 4 层表皮，这种探针对 ATR-FTIR 光谱具有重大影响，总厚度约为 60μm，超过了消逝波的理论穿透深度约 20 倍。总的来说，我们的数据表明，ATR-FTIR 光谱学中的理论和实践之间存在重大差异，并为一般来说，植物叶片光谱不能仅由角质层的结构和组成来完全解释提供了有力证据。
