Detection of exogenous sugars in pineapple juice using compound-specific stable hydrogen isotope analysis

An improved procedure for determining 2H/1H isotope ratios, using gas chromatography-isotope ratio mass spectrometry, has been used to detect the addition of exogenous C4-plant-derived sugars to pineapple juice. Isotopic techniques are commonly used to identify the addition of low-cost sugars to fruit juices and are difficult to subvert as it is not economically viable to change the isotopic ratios of the sugars. However, the addition of cane sugar to pineapple juice has presented a significant challenge that is only detected by site-specific 13C analysis of the methyl and methylene positions of ethanol derived from pineapple sugars, measured by nuclear magnetic resonance. This new GC-IRMS-based procedure utilises the trifluoroacetate derivative of sucrose to allow direct measurement of the carbon-bound non-exchangeable hydrogen. This provides advantages over alternative isotopic methods in terms of analysis time and sensitivity. This feasibility study has demonstrated the potential to reliably differentiate between authentic pineapple juices and those adulterated with commercial beet and cane sucrose.

Compound-specific δ2H using analytical pyrolysis (Py-CSIA) for assessing source and processes of soil organic matter driven by climatic changes within a Mediterranean evergreen oak forest (dehesas)

<p>Soil organic matter (SOM) is composed of multiple components from the living material, such as phenolic compounds, organic acids, lipids, peptides, polyesters, etc. A relevant part of these compounds forms part of supramolecular structures or mineral associations. Non-exchangeable hydrogen in SOM compounds is worth of study as an approach to estimate dynamic processes such as stabilization, mineralization, or biodegradation. The determination of H isotopes in SOMs faces analytical challenges related with e.g., the strength of the H bond, its exchangeability with ambient H from water or the instability of the isotopic analysis [1]. Nonetheless, along with the study of C isotopes, the study of H isotopes may certainly result in a complementary to give some light in this complex system, estimate the fate of organic compounds, and to better understand the link between hydrogen and carbon cycles in SOM [2].</p><p>In this communication, we describe and validate a methodology based on analytical pyrolysis for the direct measure of compound-specific H isotope composition (δ<sup>2</sup>H) in soil samples. The technique combines Py-GC with a high-temperature conversion reactor and a continuous flow isotope ratio mass spectrometer (IRMS) (Py-GC-HTC-IRMS).</p><p>Composite <em>dehesa</em> surface (0-10 cm) soil samples (Pozoblanco, Córdoba, Spain) were taken from four forced climatic treatment plots representing warming (W), drought (D), its combination (W+D), and control (D), installed in two different habitats: under evergreen oak canopy and in the open pasture. The samples were analysed in triplicate by conventional analytical pyrolysis (Py-GC/MS) and in parallel for δ<sup>2</sup>H Py-CSIA using the same chromatographic conditions and separation column type.</p><p>Up to 32 compounds were identified by Py-GC/MS, which H isotope composition corresponded presumably to non-exchangeable H, and with origin mainly from lignin (G- and S- units) and lipids. The H isotope composition showed an estimated average of -55 ‰ ± 7.09 for G-lignin units, -64 ‰ ± 8.64 S-lignin units and lighter -112 ‰ ± 4.32 for fatty acids (-109 ‰ ± 3.65) and the n-alkane series (C-19 to C-31). Significant differences are reportedly driven by the differences in habitat: more depleted δ<sup>2</sup>H values were found in SOM produced in the open pasture than under the tree canopy. In addition, a δ<sup>2</sup>H enrichment is observed for lignin-derived compounds in SOM under the W+D treatment.</p><p>The technique used and tested is expected to bring novelty results in relation to the processes affecting the isotopic composition of non-exchangeable hydrogen exerted by climatic treatments on diverse SOM specific compounds. Besides presenting the analytical challenges that are faced, we will discuss the effects of canopy and climatic treatments to tackle potential harsh climatic conditions as predicted, especially in Mediterranean areas. </p><p><strong>Acknowledgement:</strong> INTERCARBON project (CGL2016-78937-R), DECAFUN (CGL2015-70123-R). MICIU for funding FPI research grants (BES-2017-07968). Mrs Desiré Monis, Mrs Alba M. Carmona & Mr Eduardo Gutiérrez González are acknowledged for technical assistance.</p><p>[1] Paul, A. et al (2016). <em>Biogeosciences, 13</em>, 6587–6598.</p><p>[2] Seki, O. et al (2010). <em>Geochimica et Cosmochimica Acta, 74</em>(2), 599-613.</p>

Is It Possible to Measure Monobromamine Using Colorimetric Methods Based on the Berthelot Reaction, Like for Monochloramine?

Analytical methods based on the Berthelot reaction were recently adapted for determining monochloramine (MCA: NH2Cl) in freshwater. The specificity of the Berthelot reaction with regard to MCA is related to the need for two exchangeable hydrogen atoms to form indophenol blue. MCA can thus be distinguished from organic N-chloramines, which have only one exchangeable hydrogen atom. Monobromamine (MBA: NH2Br) may be formed during chlorination of seawater containing ammonium ions. Quantifying MBA is quite challenging and no method has been reported for its specific determination in seawater. As MBA also has two exchangeable hydrogen atoms, its reactivity might be analogous to that of MCA, but this hypothesis has never been investigated. The aim of this study was to examine the applicability of the so-called “indophenol method” for the determination of the MBA in freshwater and seawater samples. The reaction between MBA and Berthelot reagents was studied in both ultrapure water and artificial seawater. The reaction products were characterized by using gas chromatography coupled to mass spectrometry (GC–MS), Fourier transform-ion cyclotron resonance mass spectrometry (FT–ICR MS), and UV–vis spectroscopy. Results showed that colorimetric methods based on the Berthelot reaction were not suitable for measuring MBA in freshwater or seawater, since NH2Br reacts with alkaline phenol derivative via electrophilic substitution to form ortho- and para-brominated phenols instead of forming indophenol.

New method for hydrogen isotope analysis of non-structural carbohydrates

<p>Analysing stable isotope composition of biologic components can be a powerful tool to reconstruct past environmental conditions, physiological responses, and to trace metabolic pathways. The analysis of the carbon-bound non-exchangeable hydrogen isotope ratios (δ<sup>2</sup>H<sub>NE</sub>) in carbohydrates can be challenging, partly due to the exchangeability of oxygen-bound hydrogen in the same molecule with those in water or vapour. To eliminate such sample alterations, carbohydrates have been nitrated to substitute exchangeable hydrogen with nitrate ester. However, the nitration of carbohydrates is time consuming, needs high sample amount, has several safety issues, and the nitrated products of short-chained carbohydrates are instable. δ<sup>2</sup>H<sub>NE</sub> of sugars derived from living organisms or directly from the environment are thus still limited and not widespread available. Here we optimized recent δ<sup>2</sup>H<sub>NE</sub> methods, with the focus on plant-derived non-structural carbohydrates such as starch, sugars, and sugar alcohols. The exchangeable hydrogen is replaced via equilibration with water vapour of a known isotopic composition to calculate δ<sup>2</sup>H<sub>NE</sub>. In this presentation, we will explain the new δ<sup>2</sup>H<sub>NE</sub> method, discuss precision, accuracy, as well as referencing strategies, and give a first outlook for future applications in plant and environmental sciences.</p>

A novel method to quantify exchangeable hydrogen fraction in organic matter

<p>Stable isotope measurements of nonexchangeable hydrogen (<em>δ</em><sup>2</sup>H<sub>n</sub>) of bulk organic matter has emerged as a tool, with a wide range of applications in biology, biogeochemistry and forensics. However, reproducible and precise measurements of <em>δ</em><sup>2</sup>H<sub>n </sub>between laboratories and methods are still challenging. One of the largest impediments to obtain accurate isotope ratios is to use reference materials of similar exchangeable hydrogen fraction (f<sub>x</sub>) to the matrix of interest. The organic matter has typically three pools of hydrogen (H): (i) the adsorbed water, which can be minimized by extensive drying, (ii) the carbon bound H (the fraction of interest), which is non-exchangeable and cannot be removed and (iii) the non-carbon bound H, (i.e. N-, COO-, O-, and S-bound H) that cannot be removed but can be readily exchanged with the environmental moisture. Quantification of f<sub>x </sub>based on dual water vapor isotope exchange and Isotope Ratio Mass Spectrometry (IRMS) have shown large variability in f<sub>x </sub>between studies for the same organic matter type such as keratin. High variability in f<sub>x </sub>between samples and standards can translate into a large impact on the measured isotopic values. Here we used a novel approach to independently quantify f<sub>x </sub>in 21 natural organic material sources with minimal sample manipulation based on <sup>1</sup>H-<sup>2</sup>H exchange experiments and quantified through proton based liquid-state nuclear magnetic resonance (<sup>1</sup>H-NMR) spectroscopy. The experiments were carried out at room temperature by immersing separate solid powdered samples in deuterated dimethylsulfoxide (background) and deuterium oxide (<sup>2</sup>H source) followed by the quantification of the water generated in the supernatant fraction through <sup>1</sup>H-NMR using glucose as reference. At the same time, samples were analyzed through the most recent procedure of dual water vapor isotope equilibration method using online drying and equilibration in a UniPrep carousel. We discuss these findings and suggest that the proposed <sup>1</sup>H-NMR method of quantifying f<sub>x </sub>is an independent and novel approach that can contribute to a better understanding of H exchangeability in a wider range of organic materials, critical for accurate measurement of the <em>δ</em><sup>2</sup>H<sub>n</sub>.</p>

A novel thermoplastic shape memory polymer with solid-state plasticity derived from exchangeable hydrogen bonds

Thermoplastic SMP equipped with a combination of performances including inherent reprocessability, satisfactory shape memory ability and swift shape re-configurability in the solid state.

Hydrogen dynamics in soil organic matter as determined by ¹³C and ²H labeling experiments

Understanding hydrogen dynamics in soil organic matter is important to predict the fate of 3H in terrestrial environments. One way to determine hydrogen fate and to point out processes is to examine the isotopic signature of the element in soil. However, the non-exchangeable hydrogen isotopic signal in soil is complex and depends on the fate of organic compounds and microbial biosyntheses that incorporate water-derived hydrogen. To decipher this complex system and to understand the close link between hydrogen and carbon cycles, we followed labeled hydrogen and labeled carbon throughout near-natural soil incubations. We performed incubation experiments with three labeling conditions: 1 – 13C2H double-labeled molecules in the presence of 1H2O; 2 – 13C-labeled molecules in the presence of 2H2O; 3 – no molecule addition in the presence of 2H2O. The preservation of substrate-derived hydrogen after 1 year of incubation (ca. 5 % in most cases) was lower than the preservation of substrate-derived carbon (30 % in average). We highlighted that 70 % of the C–H bonds are broken during the degradation of the molecule, which permits the exchange with water hydrogen. Added molecules are used more for trophic resources. The isotopic composition of the non-exchangeable hydrogen was mainly driven by the incorporation of water hydrogen during microbial biosynthesis. It is linearly correlated with the amount of carbon that is degraded in the soil. The quantitative incorporation of water hydrogen in bulk material and lipids demonstrates that non-exchangeable hydrogen exists in both organic and mineral-bound forms. The proportion of the latter depends on soil type and minerals. This experiment quantified the processes affecting the isotopic composition of non-exchangeable hydrogen, and the results can be used to predict the fate of tritium in the ecosystem or the water deuterium signature in organic matter.