Direct quantitative analysis of biogenic silica in marine sediments by Attenuated Total Reflection Fourier Transform Infrared spectroscopy.

Biogenic silica is the major component of the external skeleton of marine micro-organism, such as diatoms, which, after the organisms' death, settle on the seabed. These micro-organisms are involved in the CO2 cycle because they remove it from the atmosphere by photosynthesis. The biogenic silica content in marine sediments, therefore, is a useful index of primary productivity in present and past epochs, which is useful to study the CO2 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 due 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 combining Multivariate Standard Addition Method (MSAM) with 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 comparable with the ones 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.