Quantification of Iron in Seawater at the Low Picomolar Range Based on Optimization of Bromate/Ammonia/Dihydroxynaphtalene System by Catalytic Adsorptive Cathodic Stripping Voltammetry

A new analytical protocol for the challenging analysis of total dissolved iron at the low picomolar level in oceanic waters suitable for onboard analysis is presented. The method is based on the revision of the adsorptive properties of the iron/2,3-dihydroxynaphthalene (Fe/DHN) complexes on the hanging mercury drop electrode with catalytic enhancement by bromate ions. Although it was based on a previously proposed reagent combination, we show here that the addition of an acidification/alkalinization step is essential in order to cancel any organic complexation, and that an extra increment of the pH to 8.6-8.8 leads to the definition of a preconcentration-free procedure with the lowest detection limit described up to now. For total dissolved iron analysis, samples were acidified to pH 2.0 in the presence of 30 \u3bcM DHN and left to equilibrate overnight. A 10 mL sample was subsequently buffered to a pH of 3c8.7 in the presence of 20 mM bromate: a 60 s deposition at 0 V led to a sensitivity of 34 nA nM-1 min-1, a 4-fold improvement over previous methods, that translated in a limit of detection of 5 pM (2-20 fold improvement). Several tests proved that a nonreversible reaction in the time scale of the analysis, triggered by the acidification/alkalinization step, was behind the signal magnification. The new method was validated onboard via the analysis of reference material and via intercalibration against flow injection analysis-chemiluminescence on Southern Ocean surface samples

New macrocyclic receptors and their metal complexes

[Resumen] Este proyecto de investigación tiene por objeto el diseño, síntesis y caracterización de receptores macrocíclicos para una coordinación adecuada de ciertos centros metálicos de entornos coordinativos. Estos receptores fueron preparados por ciclocondensación de la correspondiente dicarbonilo y el precursor de la diamina y posteriormente funcionalizados con grupos amida, ureas y tioureas... con aplicabilidad en el reconocimiento aniónico. Estos estudios son de interés en los campos biológicos, químicos y ambientales. La caracterización de los complejos metálicos macrocíclicos y sus receptores se realizó mediante técnicas de: análisis elemental; conductividad, espectrometría de masas (EI), espectroscopia vibracional (IR), espectroscopia de RMN (1H, 13C). Una vez sintetizados los correspondientes complejos metálicos y realizados los estudios de sus estructuras en estado sólido y en solución, así como sus propiedades, se analizaron sus actividades biológicas. En particular, se estudió la posible actividad catalasa de los compuestos sintetizados, realizando mediciones de la actividad enzimática in vitro donde se cuantificó con el kit AmplexRed® fluorescente.[Resumo] Este proxecto de investigación ten por obxectivo o deseño, síntese e caracterización de receptores macrocíclicos para a axeitada coordinación de certos centros metálicos de entornos coordinativos. Estes receptores foron preparados por ciclocondensación do correspondiente dicarbonilo e o precursor da diamina e posteriormente funcionalizados con grupos amida, ureas e tioureas... con aplicabilidade no recoñecemento aniónico. Este tipo de estudos son de interese nos campos biolóxicos, químicos e ambientais. A caracterización dos complexos metálicos macrocíclicos e os seus receptores realizouse mediante as técnicas de: analisise elemental; medicións de conductividade, espectrometría de masas (EI), espectroscopia vibracional (IR), espectroscopia de RMN (1H, 13C). Unha vez sintetizados os correspondentes complexos metálicos e realizados os estudos das súas estructuras no estado sólido e en disolución, así como as súas propiedades, analizáronse as actividades biolóxicas. En particular, estudouse a posible actividade catalasa dos compostos sintetizados, realizando medicións da actividade enzimática in vitro onde se cuantificou co kit AmplexRed® fluorescente.[Abstract] This research project is aimed at the design, synthesis and characterization of macrocyclic receptors for adequate coordination of certain metal centers in coordinative environments. These receptors were prepared by cyclocondensation of the corresponding dicarbonyl and diamine precursors, and subsequently functionalized with pendant- arms containing amide groups, ureas, thioureas ... with applicability in the anionic recognition. These kind of studies are of interest not only in the chemical but also in the biological and environmental fields. The characterization of the macrocyclic metal complexes and their receptors was performed using different techniques: elemental analysis; conductivity measurements, mass spectrometry (EI), vibrational spectroscopy (IR), NMR spectroscopy (1H, 13C). Once synthesized corresponding metal complexes, and studied their structures in solid state and in solution, as well as their properties, their biological activity was analyzed. In particular, we have studied the possible "catalase-like" activity of the synthesized compounds performing measurements of enzyme activity in vitro with fluorescent AmplexRed® kit was quantified.Traballo fin de grao (UDC.CIE). Química. Curso 2015/201

Carbon dioxide system in the Canary region during October 1995

During the cruise F/S Poseidon 212/3 (September 30-October 8, 1995) determination of carbon system variables was carried out over the section of La Palma-La Graciosa and at the ESTOC station in the Canary Island area. Total alkalinity and pH in the total scale at 25 degreesC were determined at 24 stations from surface to bottom. In this area, the presence of different water masses can be traced by the carbon system variables. NACW is defined by a strong gradient of A(T) and pH from 150 to 750 m. MW is characterised by high values of A(T) and pH between 1000 to 1200 in and AAIW signals are found at around 900 in in the strait between Gran Canaria and Fuerteventura with low A(T), low pH and a maximum of fCO(2). Assuming an atmospheric mean value of fCO(2) of 360 mu atm and an average surface value of 393 +/-7 mu atm, we can conclude that during this cruise this oceanic area tends to release CO2 into the atmosphere, acting as a weak source with a carbon flux towards the atmosphere of +8.0 +/-1.8 mmol.m(-2)d(-1). The saturation levels in the Canary Island area have been found to be higher than 3600 m for calcite and 2700 in for aragonite. The inorganic carbon/organic carbon ratio (IC/OC) varies from 0.07 at 300 m to 0.5 at 3000 m. The IC/OC ratio shows that about a 34% increase in the C-T of the deep water is contributed by the inorganic CaCO3 dissolution. The IC at 300 in is around 7 mu mol kg(-1), increasing with depth to 37.5 mu mol kg(-1) at 3700 m

Iron organic speciation during the LOHAFEX experiment: Iron ligands release under biomass control by copepod grazing

The LOHAFEX iron fertilization experiment consisted in the fertilization of the closed core of a cyclonic eddy located south of the Antarctic Polar Front in the Atlantic sector of the Southern Ocean. This eddy was characterized by high nitrate and low silicate concentrations. Despite a 2.5 fold increase of the chlorophyll-a (Chl-a) concentrations, the composition of the biological community did not change. Phytoplankton biomass was mostly formed by small autotrophic flagellates whereas zooplankton biomass was mostly comprised by the large copepod Calanus simillimus. Efficient recycling of copepod fecal pellets (the main component of the downward flux of organic matter) in the upper 100–150 m of the water column prevented any significant deep export of particulate organic carbon (POC). Before fertilization, dissolved iron (DFe) concentrations in the upper 200 m were low, but not depleted, at ~0.2 nM. High DFe concentrations appeared scattered from day 14 onwards as a result of the grazing activity. A second fertilization on day 21 had no significant effect on the DFe and Chl-a standing stocks. Work with unfiltered samples using different acidification protocols revealed that, by midway of LOHAFEX, rapid recycling of iron-replenished copepod fecal pellets explained the source of bioavailable iron that prolonged the duration of the bloom for many weeks. Here we present the evolution of the organic speciation of iron in the upper 200 m of the water column during LOHAFEX by a Competing Ligand Equilibrium method using voltammetry. During the first 12 days of the experiment, ligands of an affinity for iron similar to the ligands found before fertilization (logK′Fe′L~11.9) accumulated in fertilized waters mostly in the upper 80 m (from ~1 nM to ~2.5 nM). The restriction of ligand accumulation to the depth of Chl-a penetration points to exudation by the growing autotrophic population as the initial source of ligands. From day 5 onwards, we found in many samples a new class of ligands (L1) characterized by a significant higher conditional stability constant than the background complexation (logK′Fe′L1~12.9). During the middle section of the experiment (days 12 to 25) the accumulation of overall ligands and specifically L1, reached an upper limit in surface waters (at ~3 nM). Overall ligands and L1 accumulation was also observed below the mixed layer depth indicating that grazing was the process behind ligand release. During the last 10 days of the experiment ligands kept accumulating in deep waters but suffered a small decrease in the upper 50 m of the water column caused by the vanishing of L1. Ligand removal restricted to the euphotic layer was probably caused by photodegradation. A high correlation between [DFe] and [L1] suggested that recycled iron (released during grazing and copepod fecal pellet cycling) was in the form of FeL1 complexes. We hypothesize that the iron binding ligands released to the dissolved phase during LOHAFEX were mostly photosensitive intracellular ligands rapidly degraded in extracellular conditions (e.g.: pigments). Sloppy feeding by copepods and recycling of cells and cellular material in copepod fecal pellets caused the transfer of particulate ligands to the dissolved phase as zooplankton built up as a response to the blooming community

Controls of primary production in two phytoplankton blooms in the Antarctic Circumpolar Current

The Antarctic Circumpolar Current has a high potential for primary production and carbon sequestration through the biological pump. In the current study, two large-scale blooms observed in 2012 during a cruise with R.V. Polarstern were investigated with respect to phytoplankton standing stocks, primary productivity and nutrient budgets. While net primary productivity was similar in both blooms, chlorophyll a –specific photosynthesis was more efficient in the bloom closer to the island of South Georgia (39 °W, 50 °S) compared to the open ocean bloom further east (12 °W, 51 °S). We did not find evidence for light being the driver of bloom dynamics as chlorophyll standing stocks up to 165 mg m-2 developed despite mixed layers as deep as 90 m. Since the two bloom regions differ in their distance to shelf areas, potential sources of iron vary. Nutrient (nitrate, phosphate, silicate) deficits were similar in both areas despite different bloom ages, but their ratios indicated more pronounced iron limitation at 12 °W compared to 39 °W. While primarily the supply of iron and not the availability of light seemed to control onset and duration of the blooms, higher grazing pressure could have exerted a stronger control toward the declining phase of the blooms

Exploratory evaluation of iron and its speciation in surface waters of Admiralty Bay, King George Island, Antarctica

Abstract The determination of dissolved iron concentrations and speciation was conducted for the first time in surface seawater coastline samples collected during the austral summer of 2020 in Admiralty Bay, King George Island, Antarctica. The technique of competitive ligand exchange/adsorptive cathodic stripping voltammetry with 2,3-dihydroxynaphthalene as the competing ligand was evaluated, showing a sensitivity between 14.25 and 21.05 nA nmol L-1 min-1, with an LOD of 14 pmol L-1 and a mean blank contribution of 0.248 nmol L-1. Physicochemical parameters such as pH (7.85 ± 0.2), salinity (32.7 ± 0.8) and dissolved oxygen (51.3 ± 26.6%) were compatible with those of the literature; however, the average temperature (4.2 ± 0.8 °C) was higher, possibly as a reflection of global warming. The dissolved iron mean value was 18.9 ± 6.1 nmol L-1, with a total ligand concentration of 23.6 ± 12.2 nmol L-1 and a conditional stability complex constant of 12.2 ± 0.2, indicating humic substances as possible ligands. On average, the calculated free iron concentrations were 0.7 ± 0.3 pmol L-1. Relatively high concentrations of iron indicate a possible local source of Fe, likely predominantly from upwelling sediments and secondarily from ice-melting waters, which does not limit the growth of the phytoplankton

Importance of deep mixing and silicic acid in regulating phytoplankton biomass and community in the iron-limited Antarctic Polar Front region in summer

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