Attenuated Total Reflection (ATR) Micro-Fourier Transform Infrared (Micro-FT-IR) Spectroscopy to Enhance Repeatability and Reproducibility of Spectra Derived from Single Specimen Organic-Walled Dinoflagellate Cysts

Abstract

The chemical composition of recent and fossil organic-walled dinoflagellate cyst walls and its diversity is poorly understood and analyses on single microscopic specimens are rare. A series of infrared spectroscopic experiments resulted in the proposition of a standardized attenuated total reflection micro-Fourier transform infrared-based method that allows the collection of robust data sets consisting of spectra from individual dinocysts. These data sets are largely devoid of nonchemical artifacts inherent to other infrared spectrochemical methods, which have typically been used to study similar specimens in the past. The influence of sample preparation, specimen morphology and size and spectral data processing steps is also assessed within this methodological framework. As a result, several guidelines are proposed which facilitate the collection and qualitative interpretation of highly reproducible and repeatable spectrochemical data. These, in turn, pave the way for a systematic exploration of dinocyst chemistry and its assessment as a chemotaxonomical tool or proxy.

Micro-Fourier transform infrared spectroscopy of degradation-resistant organic microfossils; Influence of preservation environment and phylogeny

“…It also became clear that spectra of multiple specimens of the same species might show large variability. Recently, it has been shown that a major part of this variability might be induced by the cyst preparation methods and the way cysts have been measured with transmission or ATR modes (Meyvisch et al, 2022). Meyvisch et al (2022) clearly showed that measuring cysts with ATR consistently gave a higher repeatability and reproducibility over spectra collected in transmission modes.…”

“…Recently, it has been shown that a major part of this variability might be induced by the cyst preparation methods and the way cysts have been measured with transmission or ATR modes (Meyvisch et al, 2022). Meyvisch et al (2022) clearly showed that measuring cysts with ATR consistently gave a higher repeatability and reproducibility over spectra collected in transmission modes. They found that the use of ATR largely reduced the signal-noise ratio by reducing the number of scattering artefacts.…”

“…Furthermore, the absorption minimum at 1483 cm -1 was much less pronounced as was the absorption between 3650-2700 cm -1 . Meyvisch et al (2022) showed that especially absorptions between 3650-2700 cm -1 can vary largely when measured in transmission mode. Therefore, we assume that the observed differences with our results can be ascribed to the differences in measuring method.…”

“…The fingerprint area represents that part of the spectra where absorption patterns differ between species (e.g. Meyvisch et al, 2022). For reasons given below, spectra from Impagidinium patulum from sample 664 measured on 28-11-2021 have been excluded from analysis.…”

“…Morover, it has been useful to determine characteristic differences in the most labile and resistant dinoflagellate cyst species (Bogus et al, 2014). However, interpretation of the micro-FTIR spectra has not always been straightforward due to analytical difficulties such as Mie scattering (e.g., Blümel et al, 2018) and different methodological approaches (e.g., Meyvisch et al, 2022). Nevertheless, the use of attenuation total reflection (ATR) rather than the transmission or reflection modi circumvents most problems of Mie scattering and the method has successfully been used to determine alteration in molecular characteristics as a result of early diagenetic processes in different redox environments (Versteegh et al, 2020).…”