Fluoridic Acid in the Infrared Spectroscopy Analysis of Chemical Composition of Organic Matter

Abstract Fourier transform infrared spectroscopy (FTIR) assists in investigating functional groups of soil organic matter (SOM). However, the use of this tool is impaired given the low organic carbon levels and high content of oxides in tropical soils, resulting in low quality spectra and in turn requiring the use of hydrofluoric acid (HF). The objective of this study was to verify the efficiency of using HF in removing the mineral fraction and to increase the C concentration to enable visualizing the bands related to SOM in infrared spectra in soil samples under forest system. The HF treatment was efficient in removing mineral components and proportionally increasing C. The FTIR with HF enabled identifying differences between coarse and fine fractions. The spectra of the HF samples showed that the coarse fractions presented bands related to aromatic material and the fine fractions presented more labile components, with the absence of more recalcitrant components.