Labeling nitrogen species with the stable isotope 15N for their measurement by separative methods coupled with mass spectrometry: A review

What is the role of nitrate/nitrite in trace organic contaminants degradation and transformation during UV-based advanced oxidation processes?

The effectiveness of UV-based advanced oxidation processes (UV-AOPs) in degrading trace organic contaminants (TrOCs) can be significantly influenced by the ubiquitous presence of nitrate (NO3-) and nitrite (NO2-) in water and wastewater. Indeed, NO3-/NO2- can play multiple roles of NO3-/NO2- in UV-AOPs, leading to complexities and conflicting results observed in existing research. They can inhibit the degradation of TrOCs by scavenging reactive species and/or competitively absorbing UV light. Conversely, they can also enhance the elimination of TrOCs by generating additional •OH and reactive nitrogen species (RNS). Furthermore, the presence of NO3-/NO2- during UV-AOP treatment can affect the transformation pathways of TrOCs, potentially resulting in the nitration/nitrosation of TrOCs. The resulting nitro(so)-products are generally more toxic than the parent TrOCs and may become precursors of nitrogenous disinfection byproducts (N-DBPs) upon chlorination. Particularly, since the impact of NO3-/NO2- in UV-AOPs is largely due to the generation of RNS from NO3-/NO2- including NO•, NO2•, and peroxynitrite (ONOO-/ONOOH), this review covers the generation, properties, and detection methods of these RNS. From kinetic, mechanistic, and toxicologic perspectives, future research needs are proposed to advance the understanding of how NO3-/NO2- can be exploited to improve the performance of UV-AOPs treating TrOCs. This critical review provides a comprehensive framework outlining the multifaceted impact of NO3-/NO2- in UV-AOPs, contributing insights for basic research and practical applications of UV-AOPs containing NO3-/NO2-.

Challenging development of storable particles for oral delivery of a physiological nitric oxide donor

Nitric oxide (NO) deficiency is often associated with several acute and chronic diseases. NO donors and especially S-nitrosothiols such as S-nitrosoglutathione (GSNO) have been identified as promising therapeutic agents. Although their permeability through the intestinal barrier have recently be proved, suitable drug delivery systems have to be designed for their oral administration. This is especially challenging due to the physico-chemical features of these drugs: high hydrophilicity and high lability. In this paper, three types of particles were prepared with an Eudragit® polymer: nanoparticles and microparticles obtained with a water-in-oil-in-water emulsion/evaporation process versus microparticles obtained with a solid-in-oil-in-water emulsion/evaporation process. They had a similar encapsulation efficiency (around 30%), and could be freeze-dried then be stored at least one month without modification of their critical attributes (size and GSNO content). However, microparticles had a slightly slower in vitro release of GSNO than nanoparticles, and were able to boost by a factor of two the drug intestinal permeability (Caco-2 model). Altogether, this study brings new data about GSNO intestinal permeability and three ready-to-use formulations suitable for further preclinical studies with oral administration.

Metabolic analysis of efficient methane production from food waste with ethanol pre-fermentation using carbon isotope labeling

Anaerobic digestion (AD) has been widely applied as an economic option for food waste (FW) treatment. In this study, the group treated with ethanol pre-fermentation (EP) for 12 h (EP12) exhibited the highest cumulative biogas yield (206 mL/g-volatile solid) during AD process and therefore it was used to illuminate the underlying metabolic processes of AD with EP. Carbon isotope labeled glucose was supplemented to FW substrate, and the EP process was found to alleviate the acidification inhibition with conducting extremely high carbon flux towards ethanol formation (43.7%). Then an efficient acetogenesis phase was also observed in EP12 group, because of high carbon conversion rate from ethanol to acetate. Overall, higher carbon conversion rate to methane (90.1%) during methanogenesis was found in the AD system with EP than in the control experiment (80.3%). Thus, we quantitatively confirmed that EP affects the AD metabolism of FW in terms of carbon flow distribution.

15N-labelled nitrite/nitrate tracer analysis by LC-MS/MS: Urinary and fecal excretion of nitrite/nitrate following oral administration to mice

Determination of the modulation of nitrite and nitrate levels in biological samples usually poses a major challenge, owing to their high background concentrations. To effectively investigate the variation of nitrite/nitrate in vivo, in this study, we developed a¹⁵N-labelled nitrite/nitrate tracer analysis using LC-MS/MS following the derivatization with 2,3-diaminonaphthalene. This method allows for the determination of ¹⁵N-labelled nitrite/nitrate as ¹⁵N-2,3-naphthotriazole (¹⁵N-NAT) that can efficiently differentiate newly introduced nitrite/nitrate from the background nitrite/nitrate in biological matrices. We also investigated the contribution of background ¹⁴N-NAT isotopomers to ¹⁵N-NAT, which has long been overlooked in the literature. Our results indicated that the contribution of background ¹⁴N-NAT isotopomers to ¹⁵N-NAT is significant. Such contribution is constant (~2.2% under positive ion mode and 1.1% under negative ion mode), and does not depend upon the concentration of ¹⁴N-NAT or the sample matrix measured. An equation has been therefore developed, for the first time, to correct the contribution of background ¹⁴N-NAT isotopomers to ¹⁵N-NAT. With the proposed ¹⁵N-labelled nitrite/nitrate tracer analysis, the amount and percentage distribution of ¹⁵NO₂^- and ¹⁵NO₃^-, both in urine and feces, after oral administration of ¹⁵N-labelled nitrite/nitrate are clearly demonstrated. The excretions of ¹⁵NO₂^- and ¹⁵NO₃^- were significantly increased with the increasing dose implying that the dietary nitrite/nitrate intake is an important source in urine/feces. The present method allows for the simple, reliable and accurate quantification of ¹⁵NO₂^- and ¹⁵NO₃^-, and it should also be useful to trace the biotransformation of nitrite and nitrate in vivo.