Analysis of carbon forms in chemically-modified peat humic acids by partial least squares regression analysis of solid-state nuclear magnetic resonance spectra

Abstract

Classical structural studies on soil organic matter often show that the natural variability in C- and N forms in soil humic acids (HAs) is in many cases not enough to distinguish significant differences amongst HAs from different origin. In the present research contrasting C-distribution patterns are obtained when the HAs are modified in the laboratory through chemical treatments (derivatization reactions or methods focused to incorporation or removal of specific structural constituents). For instance, oxygen functionality can be modified by introducing or blocking the major functional groups (methylation, acetylation, oximation, nitration, sulphonation, etc). Other treatments lead to selective hydrolysis or drastic peroxydation of the HA carbon backbone. Apart this, N-groups can be introduced in the HA structure by e.g., nitration, oximation, amidation or ammonification