Spectroscopic Analysis of the Natural Organic Matter of Chernozems with Separation by Track-Etched Membranes

Context/Purpose: To get reliable information on soil organic matter, its separation or fractionation is required. Membrane fractionation is applicable to particles from 10 Da to several hundred micrometers in size. The focus of the study was on typical-chernozem narrow fractions of water-extractable organic matter (WEOM) from a cascade of membrane filters. Methods: Micro-/ultrafiltration through polycarbonate and PET track-etched membranes with pore sizes of 0.01–10 µm at room temperature was used. Results/Interpretation: Narrow WEOM fractions differ significantly in both organic and mineral constituents. For macro- and microelements, Al, Fe, and Ti are primarily observed in the fractions above 0.2 µm; Ba, Mn, Si, Zn, Ca, K, S, and Mg, in < 0.2 µm. By FTIR and ICP–AES, all narrow fractions contain clay minerals of variable composition. All fractions contain intensely fluorescing humic- and tyrosine-like components with variable composition. Conclusion: Thus, WEOM of different compositions is absorbed by clay minerals of different compositions. The developed approach provides preparative isolation of WEOM fractions and expands knowledge on WEOM chemical composition and its relationship with mineral phases.