Copper complexation by thiol compounds in estuarine waters

The stability of copper complexes with thiol substances in estuarine waters was determined for the first time using a new procedure based on cathodic stripping voltammetry (CSV). The free thiol concentration was monitored during titrations with copper in the presence of a competing ligand salicylaldoxime (SA); concentrations of copper-complexing ligands and conditional stability constants were determined simultaneously but independently. The decrease in the free thiol concentration with increasing copper concentration was used as an independent measure of the thiol-complex stability. The conditional stability constant of the thiol complexes (log KCuThiol') was between 12.3 and 14.1, and decreased with increasing salinity. The copper complexing titrations were found to fit to two complexing ligands: L1 with concentrations between 10 and 33 nM, and L2 between 14 and 300 nM. The complex stability of most of the thiols was similar to that of CuL2. Titrations at different detection windows showed a shift in the thiol complex stability suggesting that a second thiol species was present. It is therefore possible that L1 is also a thiol species. The estimated thiol concentrations can account for up to half of the total ligand concentration at low to intermediate salinities and for all of the ligands at high salinities

The determination of interactions of cobalt(II) with organic compounds in seawater using cathodic stripping voltammetry

A method is presented to determine the Co-complexing capacity of seawater using cathodic stripping voltammetry (CSV) with adsorptive collection of Co (II) complexes with either nioxime or dimethylglyoxime (DMG). The method takes advantage of ligand competition for Co2+ exerted by the ligand added for CSV and natural complexing material in the seawater. Conditional stability constants for complexation of Co with nioxime and DMG in seawater of salinities between 1 and 35 were calibrated by ligand competition with EDTA. The 'detection window' of the method is determined by the Co-complexing ability of the added ligand, as expressed by the α-coefficient (=product of the conditional stability constant, KCoL, and the ligand concentration, CL) of the natural complexing ligand, L. With DMG as the added ligand, the detection window lies between 105.2 and 107.2 at a salinity of 35. The range of the detection window is shifted by varying the DMG concentration or by using nioxime for complexation of Co2+ DMG was used to determine the Co-complexing capacity in samples originating from the estuary of the Scheldt River and the Irish Sea. A variable fraction of 45-100% (average 73%) of dissolved Co was found to occur very strongly complexed. The ligand concentration was less than the Co concentration in most of the samples. Values for log KCoL were very high, and fell within in a narrow range of 15.6-17.5. The estuarine data suggest that the organically complexed Co behaves conservatively. © 1990.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

High resolution monitoring of dissolved Cu and Co in surface coastal waters of the western North Sea

This paper discusses the distribution of dissolved Cu and Co in coastal surface waters of the western North Sea. High resolution data (more than 5500 (Cu) and 12000 (Co) data points), obtained using on-line flow-analysis techniques, clearly showed enhanced trace metal levels near the coast and estuarine outflows. In an offshore direction, the high metal levels were gradually diluted with metal-depleted seawater originating in the North Atlantic. The data indicated benthic sources for Cu and Co due to diagenetic remobilisation, sediment resuspension with injection of interstitial waters into the overlaying water and/or desorption from resuspended particles. Some evidence of biological removal of dissolved Cu was apparent in offshore coastal waters with enhanced chlorophyll concentrations. The study demonstrates how high resolution trace metal data allows us to deconvolute complex metal input and removal processes in dynamic coastal waters

DETERMINATION OF ANTIMONY IN SEAWATER BY CATHODIC STRIPPING VOLTAMMETRY

The method proposes to determine subnanomolar levels of antimony in freshwater and seawater by cathodic stripping voltammetry preceded by adsorptive deposition of complexes with catechol. Dc-polarographic and cyclic voltammetric experiments indicated that the complex of catechol with Sb(III) is adsorbed prior to the scan, and is reduced to Sb(0) in a single reduction step. The optimized analytical conditions include a catechol concentration of 0.002 M and pH 6. The deposition potential is selected at -1.0 V. rather than at a more positive potential, in order to eliminate interference by uranium in seawater by including an amalgamation step in the preconcentration procedure. This is followed by a re-oxidation period of 20 s at −0.2 V to allow amalgamated Sb to become re-oxidized and form an adsorbed layer of Sb(III)-catechol complexes. The scan is then initiated in a negative direction using a linear sweep of 50 mV/s. The limit of detection lies near 0.2 nM Sb with a deposition time of 3 min, whereas the sensitivity can be increased by extending the deposition time. Interference by copper, lead and cadmium is eliminated by adding EDTA to the solution. Both Sb(III) and Sb(V) can be determined with identical sensitivity

The measurement of organically complexed Fe(II) in natural waters using competitive ligand reverse titration

Whilst there is increasing evidence for the presence of stabilized FeII associated with organic matter in aquatic environments, the absence of a reliable method for determining FeII speciation in solution has inhibited the study of this aspect of Fe biogeochemistry. A technique is described here for the determination of FeII organic complexation in natural waters that is based on competitive ligand reverse titration and a model fit to experimental results, from which ligand concentration and a conditional stability constant can be obtained. Spectrophotometry was used to detect the Ferrozine (FZ) complex with reactive FeII, which in combination with a liquid waveguide capillary cell (LWCC) enabled high sensitivity and precision measurements of FeII to be made. A series of samples was collected in the Itchen River in Southampton, UK to test the method at a wide range of salinities including river water. Levels of FeII and total dissolved Fe were within previously reported values for this system. FeII was found to occur organically complexed with values for log?K?FeIIL (conditional stability constant for FeII-natural ligand complexes) of ?8 at salinities between 0 and 21, whilst no measurable complexation was detected at a salinity of 31. This work demonstrates that spectrophotometry can be used in combination with ligand competition to investigate metal speciation in natural waters

Copper speciation in glacial stream waters of Rutor Glacier (Aosta Valley, Italy)

The chemical speciation of copper in stream waters from Rutor Glacier was determined by cathodic stripping voltammetry with ligand competition against salicylaldoxime. The complexation of salicylaldoxime was calibrated at various calcium concentrations, the major competing cation in these waters. Copper concentrations ( 3 - 7 nM) were approximately ten-fold lower than typical for rain waters in this region, indicating that copper had been removed by adsorption onto rock and other particles. Strong copper binding ligands, with log K'(CuL) = 12.5 - 12.9, were detected in all samples, including waters emerging from beneath the glacier, with no detectable change in the ligand composition down stream. The results suggest that the ligands could originate from in situ production from algae in snow and ice, or directly from the precipitation

Shape of zooplankton and retention in filter-feeding: A quantitative comparison between industril sieves and the branchial sieves of common bream (Abramis brama) and white bream (Blicca bjoerkna)

Industrial sieves retained all cycloid copepods with a width larger than their mesh size, but Daphnia, with a width up to 1.4 times the mesh size, still passed through them. Daphnia have a lower depth/width ratio than copepods (0.599 and 0.882, respectively). Therefore, Daphnia could pass through the square meshes diagonally. In filter-feeding experiments with common bream (Abramis brama), the smallest retained copepods correspondingly were about 35% less wide than the smallest retained Daphnia. White bream (Blicca bjoerkna) did not retain copepods smaller than Daphnia. In the reducible-channel model of filter-feeding, particles are retained in the channels between the medial gill rakers. The mesh size can be reduced by lowering the lateral rakers into these channels. We calculated that zooplankton depth is the critical size parameter in reduced channels and zooplankton width in unreduced channels. We found that white bream was feeding with unreduced channels and common bream with reduced channels. The depth/width ratio (35% lower in Daphnia than in copepods) therefore explains the difference in retention of copepods and Daphnia by common bream whereas no such difference was expected for white bream. The shape of zooplankton thus affects the trophic segregation and the exploitation of food resources by fish

Urinary prostaglandin excretion in pregnancy: the effect of dietary sodium restriction.

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