1,721,043 research outputs found
Fast iron speciation in seawater by catalytic Competitive Ligand Equilibration-Cathodic Stripping Voltammetry with tenfold sample size reduction
No full textIron speciation analysis in seawater is a fundamental step to understand the cycling of this element in oceanic waters, in view of its central role in regulating primary productivity and its connection to global planetary cycles. At present, analytical procedures are the bottleneck for speciation analysis, in term of both time and sample size requirement. Here we present a novel instrumental configuration for the speciation analysis of iron by the Competitive Ligand Equilibration - Cathodic Stripping Voltammetry (CLE-CSV) procedure. The new system features a 1 mL microcell and a silver wire pseudoreference enabling a tenfold reduction of the sample volume. 2,3-dihydroxynaphthalene was used as the complexing ligand and atmospheric oxygen as the catalytic enhancer because they ensured the best analytical performances in terms of detection capabilities. The side reaction coefficient for the FeDHN complex αFe'DHN was calibrated against EDTA and an average value of 9.25 for logK’Fe'DHN was calculated. The method was successfully validated in UV digested seawater using diethylenetriaminepentaacetic acid (DTPA), which has known stability constant for iron. The method was lastly applied to six samples from the Ross Sea water column (Antarctica), demonstrating its fit for purpose for the detection of trace amounts of iron ligands in seawater. Thanks to the employed instrumental configuration and the high sensitivity, the proposed method achieved a tenfold reduction in sample size, a tenfold increase in sensitivity compared with other methods employing DHN and halved the analysis time with respect to the fastest method reported in the literature. Half an hour is enough to measure a 12 point titration, making the analysis of at least three titrations per day feasible. It is expected that the application of this procedure will foster the sample throughput, thanks to the reduced analysis time, and make possible the analysis of limitedly available and challenging samples, like porewater and vent fluids via the tenfold reduction in sample size
Exploring bufferless iron speciation in seawater by Competitive Ligand Equilibration-Cathodic Stripping Voltammetry: Does pH control really matter?
No full textIron speciation in seawater is of the utmost importance as this element plays a central role in the regulation of primary productivity. Here we present the development of a CLE-CSV (Competitive Ligand Equilibration-Cathodic Stripping Voltammetry) procedure for iron speciation in seawater avoiding for the first time the use of the pH buffer (2,3-dihydroxynaphthalene is used as the added ligand, atmospheric oxygen as the catalytic enhancer and a 1 mL volume per sample aliquot). The unbuffered method was setup, validated by using known ligands and finally applied to the analysis of six seawater samples from the Ross Sea (Antarctica). The validation procedure demonstrated that ultratrace levels of ligands may be reliably determined and the application to seawater samples proved that the complex natural ligand pool can be detected with results undistinguishable from the ones obtained by the buffered procedure. The proposed method demonstrated a new principle in trace element speciation analysis by CLE-CSV, namely that the equilibration step may be performed at natural pH, whereas the pH may be set at its optimal value for sensitivity during analysis, thanks to the raise in pH at the electrode/solution interface caused by oxygen reduction. This change in paradigm paves the way to the investigation of iron speciation at natural pH in traditionally difficult samples that show circumneutral or slightly acidic pH values. The relevance of the here proposed approach to existing speciation procedures by CLE-CSV is also discussed
The use of iron chemical analysis of podzols to date the Late Pleistocene–Holocene deglaciation history of the Central Italian Alps
No full textPodzols that have developed on glacial and periglacial features provide the opportunity to reconstruct glacial evolution after the Last Glacial Maximum (LGM) using different soil indices. Analysing 17 soils classified as podzol, we used the crystallinity ratio of free iron oxides (CRF) on both the A and Bs horizons, and absolute ages for the same landforms containing the soil profile, to create dating curves. Two equations were generated: age = 4566.9 × ln (CRF) + 1760 (1), and age = 3907 × ln (CRF) + 3508.2 (2). The reliability of the curves was evaluated with the Feo/Fed ratio, and with the difference of ages calculated using both equations. Equation (2) is considered more reliable because the A horizon may be influenced by new pedogenesis on the pre-existing podzol, leading to the development of a new type of soil. By dating the soils, we reconstructed the glacial history of the three main upper branches of the LGM Adda Glacier in the Central Italian Alps, specifically the Stelvio Pass area (ST), Gavia Pass area (GV), and the Val Viola valley (VV). Seven glacial advances were identified at 16.7–14.7 ka (phase I), 12.3 ka (phase II), 11 ka (phase III), 10–9.7 ka (phase IV), 9 ka (phase V), 7.5 ka (phase VI) and 5.3 ka (phase VII). The first five phases are chronologically similar to the main Late Pleistocene–Early Holocene phases recorded in the Central European Alps. The last two Holocene phases, which are both longer in duration than the Little Ice Age, are recorded in ST and GV. Interestingly, these phases generally are not recorded in the rest of the Central European Alps, where the late Holocene glaciers were smaller than their present size
The what, how, why, and when of dendrochemistry: (paleo)environmental information from the chemical analysis of tree rings
No full textThe chemical analysis of tree rings has attracted the interest of researchers in the past five decades in view of the possibility of exploiting this biological indicator as a widely available, high-resolution environmental archive. Information regarding the surrounding environment can be derived either by directly measuring environmental variables (nutrient availability, presence of pollutants, etc.) or by exploiting proxies (e.g. paleoclimatic and paleoenvironmental reconstructions). This review systematically covers the topic and provides a critical view on the reliability of dendrochemical information. First, we introduce the determinable chemical species, such as major elements, trace metals, isotopic ratios, and organic compounds, together with a brief description of their uptake mechanisms and functions in trees. Subsequently, we present the possibilities offered by analytical techniques in the field of tree ring analysis, focusing on direct methods and recent developments. The latter strongly improved the details of the accessible information, enabling the investigation of complex phenomena associated with plant life and encouraging the direct analysis of new analytes, particularly minor organic compounds. With regard to their applications, dendrochemical proxies have been used to trace several processes, such as environmental contamination, paleoclimate reconstruction, global environmental changes, tree physiology, extreme events, ecological trends, and dendroprovenance. Several case studies are discussed for each proposed application, with special emphasis on the reliability of tracing each process. Starting from the reviewed literature data, the second part of the paper is devoted to the critical assessment of the reliability of tree ring proxies. We provide an overview of the current knowledge, discuss the limitations of the inferences that may be drawn from the dendrochemical data, and provide recommendations for the best practices to be used for their validation. Finally, we present the future perspectives related to the advancements in analytical instrumentation and further extension of application fields
Reaction-Diffusion Problems on Time-Dependent Riemannian Manifolds: Stability of Periodic Solutions
No full textWe investigate the stability of time-periodic solutions of semilinear parabolic problems with Neumann boundary conditions, posed on a domain of a Riemannian manifold. On the domain we consider metrics that vary periodically in time. The discussion is based on the principal eigenvalue of periodic parabolic operators. The study is related to biological models on the effect of growth and curvature on pattern formation. Metric properties, for instance, the Ricci curvature, play a crucial role
The Poisson equation on Riemannian manifolds with weighted Poincaré inequality at infinity
Full text linkWe prove an existence result for the Poisson equation on non-compact Riemannian manifolds satisfying weighted Poincaré inequalities outside compact sets. Our result applies to a large class of manifolds including, for instance, all non-parabolic manifolds with minimal positive Green’s function vanishing at infinity. On the source function, we assume a sharp pointwise decay depending on the weight appearing in the Poincaré inequality and on the behavior of the Ricci curvature at infinity. We do not require any curvature or spectral assumptions on the manifold. In comparison with previous works, we can deal with a more general setting on the curvature bounds and without any spectral assumption
On the critical p-Laplace equation
Full text linkIn this paper we provide the classification of positive solutions to the critical p -Laplace equation on R-n, for 1 < p < n, possibly having infinite energy. If n = 2, or if n = 3 and (3)/(2) < p < 2 we prove rigidity without any further assumptions. In the remaining cases we obtain the classification under energy growth conditions or suitable control of the solutions at infinity. Our assumptions are much weaker than those already appearing in the literature. We also discuss the extension of the results to the Riemannian setting
Strategies for the characterization and optimization of adsorptive stripping voltammetry with catalytic enhancement for ultratrace element determination: The case of iron 2,3-dihydroxynaphthalene complex with catalytic enhancement by atmospheric oxygen
No full textA comprehensive approach to the characterization and setup of metal determination by adsorptive stripping voltammetry with catalytic enhancement (CAdSV) is presented. The focus is on the understanding of the chemical features of these procedures to demonstrate which parameters can influence the analytical performances: the CAdSV method for the determination of iron at trace level using 2,3-dihydroxynaphthalene (DHN) is taken as case study. First, the ligand degradation was investigated by 1H NMR spectroscopy highlighting a significant degradation at alkaline pH of around 33% in 12 h. The use of degraded DHN had a detrimental effect on the analytical sensitivity, highlighting the need to frequently prepare the ligand. The thermodynamics of ligand and complex adsorption onto the working electrode (hanging mercury drop electrode, HMDE) was subsequently studied: both showed a strong adsorption onto the mercury surface (βDHN = 2.5·103 ± 5·102 L mol−1; βFe-DHN = 5.5·105 ± 8·104 L mol−1), but no competition for the mercury surface between the ligand and the complex was evident as determined by the multicomponent Langmuir isotherm. The mechanism of the electrode reaction was also investigated with and without the catalytic enhancement of the signal caused by air oxygen. The reduction of the complex Fe-DHN in purged solution showed α = 0.57 and k0 = 79 cm s−1, highlighting a quasireversible mechanism. The apparent catalytic constant (k'cat) was 168 s−1 for 1 mL sample volume: the simultaneous study of the kinetic and catalytic constant showed that the current signal was mostly influenced by the kinetic of the reaction
To what extent are filter feeder elasmobranchs exposed to marine pollution? A systematic review
No full textFilter feeding elasmobranchs may be considered as biological indicators of marine pollution, despite most of these species are under some degree of extinction risk. Among threats to this taxonomic group, marine pollution might represent an additional concern for their survival. In this review, a comprehensive systematic search of scientific literature on pollutants in filter feeding elasmobranchs was conducted to evaluate the bioaccumulation patterns, and risk for human consumers. We found that, despite an increasing trend in the number of published studies, the geographical coverage is still very limited and most of the studies focused solely on trace elements (70.8%). Among sharks, Rhincodon typus was the most represented species (66.7%), while Mobula mobular the most studied ray species (41.7%). Comparing the levels of pollutants in filter feeders between ocean basins, this review highlighted that Hg, As and Cd levels are mostly higher in those areas affected by both strong natural and anthropogenic source of emissions, such as the Indian Ocean. With regards to OCs, ΣPCB levels in muscle of C. maximus were between 4.3 and 50.5 μg kg-1 ww, highlighting a persistent contamination of PCB in the Mediterranean Sea. Some species exceeded the maximum allowable limits for foodstuff consumption for As, Cd and Pb. A total of 77.8% of the analyzed species exceeded the Environmental Quality Standards for Hg, while they were always below the EQSbiota for HCB, PBDEs, PFOS and DDT. Given their feeding mechanism that continuously samples the marine environment, further investigations are urgently needed to determine not only the extent of contaminant exposure in different hotspot locations but also the risks posed to the elasmobranch health
Nonexistence of solutions to quasilinear parabolic equations with a potential in bounded domains
Full text linkWe are concerned with nonexistence results for a class of quasilinear parabolic differential problems with a potential in Ω × (0 , + ∞) , where Ω is a bounded domain. In particular, we investigate how the behavior of the potential near the boundary of the domain and the power nonlinearity affect the nonexistence of solutions. Particular attention is devoted to the special case of the semilinear parabolic problem, for which we show that the critical rate of growth of the potential near the boundary ensuring nonexistence is sharp
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