FTIR spectral band shifts explained by OM–cation interactions

Background: The organic matter (OM) in soils interacts with polyvalent cations such as Ca2+ through hydroxyl (OH), carboxylic acid, ester, keto, aldehyde (summarized C=O), and carboxylate (COO?) functional groups. Such interactions affect the bonding strength of double bond between C O atom groups, which is assumed to shift wavenumber (WN) region O–H (hydroxyl), C=O, COO?, OMcat (i.e., C=O interacting plus groups) absorption band maxima Fourier transform infrared (FTIR) spectra. shifts limit evaluation spectral information on OM soil samples. Aims: objective this study was analyze extent changes intensities for relations cation concentrations, estimate effects properties potential wettability evaluated from FTIR ratios. Methods: Polygalacturonic acid (PGA) solutions were mixed a CaCl2 solution at different relations. freeze-dried mixtures analyzed spectroscopy mid-infrared range by using KBr-technique. spectra interpreted respect O–H, bands, latter reflecting formation PGA-Ca2+ complexes. Results: PGA–Ca compared that pure PGA indicate addition both, intensity WN value OMcat, COO? maxima. COO?/C–O–C ratio increased concentration while C–H/C–O–C decreased. Furthermore, shifted towards lower values, higher values. two times than maximum concentration. Conclusion: Spectral depend automated interpretations without prior soil-specific corrections.