Optimized Demineralization Technique for the Measurement of Stable Isotope Ratios of Nonexchangeable H in Soil Organic Matter

Abstract

To make use of the isotope ratio of nonexchangeable hydrogen (δ(2)H(n (nonexchangeable))) of bulk soil organic matter (SOM), the mineral matrix (containing structural water of clay minerals) must be separated from SOM and samples need to be analyzed after H isotope equilibration. We present a novel technique for demineralization of soil samples with HF and dilute HCl and recovery of the SOM fraction solubilized in the HF demineralization solution via solid-phase extraction. Compared with existing techniques, organic C (C(org)) and organic N (N(org)) recovery of demineralized SOM concentrates was significantly increased (C(org) recovery using existing techniques vs new demineralization method: 58% vs 78%; N(org) recovery: 60% vs 78%). Chemicals used for the demineralization treatment did not affect δ(2)H(n) values as revealed by spiking with deuterated water. The new demineralization method minimized organic matter losses and thus artificial H isotope fractionation, opening up the opportunity to use δ(2)H(n) analyses of SOM as a new tool in paleoclimatology or geospatial forensics.

Terrestrial support of zooplankton biomass in northern rivers

“…For additional isotopic and fatty acid analyses, POM was collected on 142 mm diameter 1.0 μm glass fiber filters (PALL A/E; PALL Life Sciences) by gentle pressure-filtration of 20 L river water (one entire cubitainer). We assumed that inorganic H associated with clay particles, which could bias the deuterium analyses (Ruppenthal et al 2013), contributed to a negligible share of the hydrogen that was captured on these 1.0 μm filters because the study catchments are characterized by glacial till soils with low clay contents. For dissolved organic matter (DOM) deuterium analysis, 1000-2000 mL of GF/F-filtered water per site was freeze dried.…”

Thermal Conversion of Municipal Biowaste Anaerobic Digestate to Valuable Char

“…This phenomenon could be attributed to a progressive inclusion of nitrogen species into cycloaliphatic and/or aromatic structures, forming a N-containing char. Additionally, the HF pretreatment of the precursor consists in a demineralization process, making the ash content in the MWDF almost negligible (below 1 wt.%) [18]. To better evaluate the chemical modifications induced by pyrolysis, FTIR spectroscopy has been used to characterize the vibrational behaviors of the two samples (MWDF and MWDF char).…”

Fingerprinting Blue Carbon: Rationale and Tools to Determine the Source of Organic Carbon in Marine Depositional Environments

“…First, isotopic composition of primary producers is not universal and second, the source materials are required to determine provenance on a case-by-case basis. Some complications such as the presence of inorganic hydrogen and the exchange of hydrogen after soil collection, may be overcome with the use of stringent extraction and drying methods (Chesson et al, 2009;Meier-Augenstein et al, 2013;Ruppenthal et al, 2013;Soto et al, 2017). However, other complications remain to be solved including measuring only a small fraction of total organic matter due to incomplete extraction (<80% of the total organic matter; Ruppenthal et al, 2013), accounting for source specific element ratios (i.e., C/H and C/O), isolating non-exchangeable H, and determining the effect of bacterial degradation on δ 2 H and δ 18 O.…”

“…Some complications such as the presence of inorganic hydrogen and the exchange of hydrogen after soil collection, may be overcome with the use of stringent extraction and drying methods (Chesson et al, 2009;Meier-Augenstein et al, 2013;Ruppenthal et al, 2013;Soto et al, 2017). However, other complications remain to be solved including measuring only a small fraction of total organic matter due to incomplete extraction (<80% of the total organic matter; Ruppenthal et al, 2013), accounting for source specific element ratios (i.e., C/H and C/O), isolating non-exchangeable H, and determining the effect of bacterial degradation on δ 2 H and δ 18 O. While these isotopic tracers are successfully used to study animal movement (Rubenstein and Hobson, 2004) and could assess food web interactions (Zanden et al, 2016), there is little or no information on how bulk values may change during decomposition.…”