ATR-FTIR Spectroscopy, a New Non-Destructive Approach for the Quantitative Determination of Biogenic Silica in Marine Sediments

• Published in: Molecules (Basel, Switzerland) Vol. 24; no. 21; p. 3927
• Main Authors: Melucci, Dora, Zappi, Alessandro, Poggioli, Francesca, Morozzi, Pietro, Giglio, Federico, Tositti, Laura
• Format: Journal Article
• Language: English
• Published: Switzerland MDPI AG 31.10.2019; MDPI
• Subjects: Antarctic Regions; Aquatic Organisms - chemistry; atr-ftir; biogenic silica; Carbon dioxide; chemometrics; diatoms; Expected values; Fourier transforms; Geography; Geologic Sediments - chemistry; Infrared reflection; Infrared spectroscopy; Marine microorganisms; Marine sediments; Methods; nas; Ocean floor; Organisms; Photosynthesis; Plankton; Polyamines; Reference Standards; Risk analysis; Sediment samplers; Sediments; Silica; Silicon Dioxide - chemistry; Spectrometers; Spectrophotometry; Spectroscopy; Spectroscopy, Fourier Transform Infrared; Vibration; Antarctic Regions; Ross Sea; Antarctica; Southern Ocean; NAS; biogenic silica; chemometrics; diatoms; ATR-FTIR
• ISSN: 1420-3049; 1420-3049
• DOI: 10.3390/molecules24213927

Biogenic silica is the major component of the external skeleton of marine micro-organisms, such as diatoms, which, after the organisms death, settle down onto the seabed. These micro-organisms are involved in the CO cycle because they remove it from the atmosphere through photosynthesis. The biogenic silica content in marine sediments, therefore, is an indicator of primary productivity in present and past epochs, which is useful to study the CO trends. Quantification of biosilica in sediments is traditionally carried out by wet chemistry followed by spectrophotometry, a time-consuming analytical method that, besides being destructive, is affected by a strong risk of analytical biases owing to the dissolution of other silicatic components in the mineral matrix. In the present work, the biosilica content was directly evaluated in sediment samples, without chemically altering them, by attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy. Quantification was performed by combining the multivariate standard addition method (MSAM) with the net analyte signal (NAS) procedure to solve the strong matrix effect of sediment samples. Twenty-one sediment samples from a sediment core and one reference standard sample were analyzed, and the results (extrapolated concentrations) were found to be comparable to those obtained by the traditional wet method, thus demonstrating the feasibility of the ATR-FTIR-MSAM-NAS approach as an alternative method for the quantification of biosilica. Future developments will cover in depth investigation on biosilica from other biogenic sources, the extension of the method to sediments of other provenance, and the use higher resolution IR spectrometers.