Luis M. Laglera

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 V ) 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. D 2003 Elsevier Science B.V. All rights reserved.

Copper adsorption in diatom cultures

Abstract The organic ligands naturally present in seawater, on the cell surface groups, and those released by the marine phytoplankton species, Thalassiosira weissflogii and Phaeodactylum tricornutum , and their physico-chemical interaction with copper ions were studied using differential pulse anodic stripping voltammetry (DPASV) as a function of pH, temperature, salinity and biomass. The acid–base properties were characterized from titration curves of diatom suspensions with proton. Three p K a values were determined for each diatom, all of which were similar. Titration curves with copper allowed us to determine the specific adsorption of copper in a heterogeneous adsorption model. An iterative method that combines both Scatchard and Van den Berg–Ruzic approaches was used in order to determine the complexing capacity and the binding constants. High-affinity surface groups of both algae have similar affinity for copper but the concentration of these groups is 45% per cell higher for P. tricornutum as compared to T. weissflogii . The low-affinity groups in T. weissflogii (9.37) have higher stability constants than those in the P. tricornutum (9.0). After 36 h equilibrium, a ligand concentration of 18.6×10 −16 M cell −1 P. tricornutum and 25.0×10 −16 M cell −1 T. weissflogii with a conditional stability constant of log K ′=9.8 and log K ′=10.0, respectively, was exuded into the original seawater. In the presence of lead, high specificity was observed for the lowest stability constant ligands for copper, while the highest stability constant ligands were affected more by the presence of lead in solution. The ligands of T. weissflogii were less affected.

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 μM DHN and left to equilibrate overnight. A 10 mL sample was subsequently buffered to a pH of ∼8.7 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.

Cadmium Adsorption by Chlamydomonas reinhardtii and its Interaction with the Cell Wall Proteins

Environmental Context. In natural waters, trace metals levels are largely controlled by microbiology; organisms take up, metabolize, store, and detoxify the metals. However, aquatic organisms may regulate their own uptake via dynamic processes that result in a system that is far from equilibrium. By examining the model title alga with a battery of techniques, a more realistic assessment of metal uptake and metal regulatory processes could be gained. Abstract. Cadmium adsorption by a wild type strain of Chlamydomonas reinhardtii and a cell wall-less mutant was quantified as a function of Cd speciation in a well-defined aqueous medium. For both strains, Cd adsorption to the cell surface was not predicted by a single-site (Langmuirian) model. Indeed, no saturation of the cell wall was observed, even for Cd concentrations in excess of 5 × 10−3 M. A continual production of Cd binding sites appeared to be responsible for the observed increase of Cd adsorption with time. SDS-page separations and measurements of the protein content of algal supernatants demonstrated that organic matter was released by the algae, both in the presence and absence of Cd. Both the nature (e.g. polysaccharides, proteins) and the quantity of exudate production was influenced by the physicochemistry of the external medium. Measurements using the permeation liquid membrane (PLM) and anodic stripping voltammetry (ASV) demonstrated that dissolved cadmium was rapidly complexed by the organic exudates produced by the algae.

Direct recognition and quantification by voltammetry of thiol/thioamide mixes in seawater.

Thiols and thioamides form part of the pool of reduced sulfur substances (RSS) that modify the health of aquatic ecosystems acting as radical scavengers and heavy metal ligands. Their concentrations could be easily determined in seawater by cathodic stripping voltammetry (CSV) were it not be for the coalescence of their responses in a single peak. Here, we modified the traditional CSV method of RSS analysis to allow individual recognition and quantification in thiol/thioamide mixes. Glutathione, cysteine, thiourea and thioacetamide in UV digested seawater were repeatedly analyzed shifting the deposition potential (E(dep)) in the range +0.07 to -0.4V at high resolution. The representation of peak height (i(p)) and peak potential (E(p)) vs E(dep) resulted in different and distinctive profiles for each substance that allowed the selection of adequate E(dep) ranges for their separate quantification. Copper saturation modified thiol profiles and cancelled the response of thioamides. The vs E(dep) profiles explained the nature of the different thiols and thioamides present in the sample and permitted their individual quantification with excellent accuracy. The utility of the method was put to test with seawater modified with natural unknown RSS from pore waters and Posidonia oceanica exudates. Although both samples gave similar CSV signals, the vs E(dep) profiles unveiled completely different electrochemical behaviors incompatible with a similar nature. Based on those profiles we hypothesized that pore waters released a glutathione/thiourea mix and that one or several unidentified RSS formed part of P. oceanica exudates. The analytical scheme proposed here opens a new door to the use of direct voltammetry in the qualitative and quantitative determination of RSS in natural waters.

Cadmium determination in natural water samples with an automatic multisyringe flow injection system coupled to a flow­through screen printed electrode

Heavy metals, as cadmium, attract a rising attention in environmental studies due to their increasing release by human activities and acute toxicity. In situ analytical methods are needed to minimize current uncertainties caused by the transport and conservation of samples. Here, we present the completely automatic determination of Cd in natural waters using a newly developed screen printed electrode sensor (SPE), inserted in a homemade purpose-built flow cell coupled to a Multi-Syringe Flow Injection Analysis system (MSFIA). The working electrode of SPEs was constituted by a carbon film modified with Nafion. Cd was plated on an in situ bismuth film and determined using Square Wave Anodic Stripping Voltammetry. Different chemical conditions of deposition and stripping were studied. A sample/acetic buffer mixture was found to be a well suited medium to form the Bi film and perform the analysis. Cd was quantified via calibration by on line standard additions. The limit of detection was found to be 0.79μgL(-1), well below the limit stipulated by the European directive (5μgL(-1)). Good sample throughput (14h(-1)) and low consumption of reagent and sample (1.3mL) were also obtained in line with previous works in Cd flow analysis.

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.

Ultrasensitive and Fast Voltammetric Determination of Iron in Seawater by Atmospheric Oxygen Catalysis in 500 μL Samples

A new method based on adsorptive cathodic stripping voltammetry with catalytic enhancement for the determination of total dissolved iron in seawater is reported. It was demonstrated that iron detection at the ultratrace level (0.1 nM) may be achieved in small samples (500 μL) with high sensitivity, no need for purging, no added oxidant, and a limit of detection of 5 pM. The proposed method is based on the adsorption of the complex Fe/2,3-dihydroxynaphthalene (DHN) exploiting the catalytic effect of atmospheric oxygen. As opposite to the original method (Obata, H.; van den Berg, C. M. Anal. Chem. 2001, 73, 2522-2528), atmospheric oxygen dissolved in solution replaced bromate ions in the oxidation of the iron complex: removing bromate reduces the blank level and avoids the use of a carcinogenic species. Moreover, the new method is based on a recently introduced hardware that enables the determinations to be performed in 500 μL samples. The analyses were carried out on buffered samples (pH 8.15, HEPPS 0.01 M), 10 μM DHN and iron quantified by the standard addition method. The sensitivity is 49 nA nM(-1) min(-1) with 30 s deposition time and the LOD is equal to 5 pM. As a result, the whole procedure for the quantification of iron in one sample requires around 7.5 min. The new method was validated via analysis on two reference samples (SAFe S and SAFe D2) with low iron content collected in the North Pacific Ocean.

The influence of zinc, aluminum and cadmium on the uptake kinetics of iron by algae

The uptake of iron by the marine diatom Thalassiosira weissflogii and the green algae Dunaliella tertiolecta in seawater has been investigated. Computations were made of the rate constants for the binding of iron to specific cell surface-associated transport ligands and the subsequent slow active uptake into the cytoplasm of the cells. Although both algae transport Fe, the sorption constants and the kinetic parameters are markedly different and temperature dependent. The sorption constants, which are one order of magnitude higher for T weissjlogii versus D. tertiolecta (2.5 X 10m9 1 cell-’ vs. 2.2 X lo-” 1 cell-‘) at 2X, give us a measure of the theoretical number of transport sites needed by each cell. The effects on the iron speciation and on the rate of iron uptake due to the addition of different concentrations of Zn(II), Al(II1) and Cd(D) have also been determined. The results confirm that while iron is taken up via specific sites on the cell surfaces, synergistic and antagonistic effects on the iron rate uptake for T. weissflogii and D. tertiolecta, respectively, have been found and evaluated. 0 1997 Elsevier Science B.V.

Cathodic pseudopolarography: a new tool for the identification and quantification of cysteine, cystine and other low molecular weight thiols in seawater.

Thiols are compounds of paramount importance in the cellular metabolism due to their double detoxifying role as radical scavengers and trace metal ligands. However, we have scarce information about their extracellular cycling as limited data are available about their concentration, stability and speciation in the aquatic medium. In natural waters, they form part of the pool of reduced sulfur substance (RSS) whose presence has been documented by voltammetric and chromatographic methods. Traditional use of cathodic stripping voltammetry (CSV) for the analysis of RSS could only give an overall concentration due to the coalescence of their CSV peaks. Recently, it has been shown that the use of multiple deposition potentials could take voltammetry of RSS to a higher level, permitting the identification and quantification of the mixtures of RSS despite showing as a single coalescent peak. Here, due to its similarity with classical pseudopolarography, we propose to rename this analytical strategy as cathodic pseudopolarography (CP) and we present for the first time its use for the analysis of mixes of low molecular weight thiols (LMWT) at the nanomolar level. Despite limitations caused by the identical behavior of some LMWT, the CP allowed to isolate the contribution of cysteine and cystine from a coalescent signal in LMWT mixtures. Sample handling with clean protocols allowed the direct determination of the cystine:cysteine ratio without sample modification. Finally, we show the application of CP to identify LMWT in seawater samples extracted from benthic chambers and suggest future applications in other areas of environmental electroanalysis.