Alberto Zirino

Remote stripping electrode for in situ monitoring of labile copper in the marine environment

A remote electrode, operated in the stripping potentiometric mode, is employed for in situ marine surveys of labile copper in bay seawater. The probe relies on a novel electrode assembly, coupled to a long shielded cable, and allows direct immersion of the gold working electrode in seawater. Continuous operation of the probe from a small boat is used for obtaining the distribution pattern of copper in San Diego Bay. Monitoring of labile copper in the unpolluted water of Sequim Bay (Washington state) is also reported. As desired for metal speciation studies, such a submersible in situ operation is performed without perturbation of the natural equilibria. Laboratory optimization, in situ characterization, and future prospects are described and discussed.

Anodic stripping peak currents: electrolysis potential relations for reversible systems

In the case of vegetation samples, a precision (as a mean relative standard deviation) of 4.3% is obtained in the range 50-600 ppm F. A corresponding value of 4.1% is obtained for soil samples in the range 30-700 ppm F. These values of 4.3 and 4.1% indicate excellent precision for the method and are a reflection of the fact that the samples undergo a minimum of handling during the analytical procedure. The precision of 4.3% for vegetation samples may be compared with a value of 5.7% reported by Jacobson and Heller (6) for an acid/alkali leach procedure using the SIE method. Summary. It is evident from the results of this work that the rapid NaOH fusion-SIE procedure described in this work is suitable for the analysis of total fluoride in both soils and vegetation. Since interfering cations can be removed, as insoluble oxides, prior to analysis, the time consuming distillation step recommended in the classical Willard-Winter procedure becomes unnecessary. Finally, the procedure can easily be extended to include the determination of total atmospheric fluoride if the sample is collected on a 0.45-p membrane filter impregnated with Na2CO:j (12). In this laboratory such filters exposed for a 7-day period at a flow rate of about 15 l./min have been satisfactorily analyzed. Under the conditions just stated, a detection limit for the ambient air of 0.01 pg F/m3 is possible. For a 24-h sampling period, the detection limit will approach 0.1 pg F/m:l. For electrochemically reversible systems, a study has been made of the relationship between peak currents obtained by anodic stripping voltammetry and the applied electrolysis potential. An equation was derived which describes these relationships as sigmoidal or polarographic curves. However, unlike polarography, is predicted to be a llnear function of the electrolysis time f. THEORY For a substance 0 which reduces to a metal Rand forms an amalgam with Hg, peak current-applied potential plots resemble polarographic curves because the relationship between the peak current and concentration (1) where i, = stripping peak current, k = a proportionality constant, q = the total charge passed for deposition of the metal, V = the solution volume, Co* = the concentration of i, = k q = knFVCo* substance 0 in the bulk of the solution and n and F have their usual meaning, is similar to the fundamental relationship of polarography i a CO*, where i is the instantaneous current for the …

Determination of copper complexation in sea water by a ligand competition technique with voltammetric measurement of the labile metal fraction

Abstract A ligand competition—anodic stripping voltammetric (ASV) technique is proposed for investigating copper complexation in sea water. Increasing amounts of ethylenediamine were used to convert the non-reducible copper fraction into a labile copper complex and the change in the stripping peak current was followed. Ligand titration of sea water using this technique indicated that the naturally occurring non-labile copper fraction is bound to ligands having concentrations less than 5 × 10 −9 M and a conditional stability constant (log K ′ CuL ) of 13.1 ± 0.3. An advantage of ligand exchange voltammetry is that when applied to raw sea water, it allows the investigation of copper ‘already” bound by inert ligands. On the other hand, when applied to copper-spiked sea-water samples, this method permits the investigation of the “newly formed” inert complexes. It was found that when copper was added to give [Cu] > × 10 −8 M, the added copper assumed a different inert form than that of the already bound copper in the sample. The combined use of ligand competition—ASV with stripping polarography as a diagnostic method of speciation analysis is discussed.

Direct measurement of Cu(II)(aq) in seawater at pH 8 with the jalpaite ion-selective electrode

Abstract The variability of measurement of the pCu of seawater at pH 8 was studied using up to 5 similar Orion 90-24, jalpaite-based electrodes. Large variability (ca. 1 pCu unit) among the values yielded by the individual electrodes was observed when the electrodes were stored in artificial seawater and exposed to light including sunlight. This variability is in agreement with mechanisms proposed previously. The variability among the electrodes was reduced to about ±0.2 pCu units when the electrodes were stored in sacrificial EN seawater solution and shielded from light. Eight measurements of San Diego Bay seawater made with an individual electrode yielded pCu=12.23±0.06 (1 σ ) regardless of the order in which the electrode was calibrated with standard buffer solutions. This degree of precision makes it possible to follow the small, time-dependent changes in the pCu of seawater. The effects of electrode rotation and the adsorption or desorption of organic matter on the electrode are presented and discussed.

Spatial and temporal variations in copper speciation in San Diego Bay

Copper in estuaries has been an issue of concern for its toxicity to marine organisms. The ability to understand the processes that control copper speciation is a key factor towards achieving an improved assessment of the ecological risk it poses in the marine environment. Field measurements were made in August 2000, January 2001, May 2001, and September 2001 to provide a comprehensive view of circulation and water quality both spatially and temporally for the entire San Diego Bay. Rapid, underway, analysis of copper provided a unique, high-resolution view of total and labile copper species. The data show that total copper concentrations in San Diego Bay have been close to or above water quality criteria, increasing gradually from the lowest values in the mouth region (8 nM) to the innermost region (approximately 55 nM) with elevated concentrations existing in the Shelter Island and Commercial Basins. This work indicates that free copper activity lies between 10−11 and 10−13, and declines from the entrance to the head of San Diego Bay, even though the total copper concentration increases, a likely result of complexation with organic and particulate matter. Free copper measurements also show a seasonal dependence with the highest concentrations occurring 2 wk after a winter rain event in January 2001, reaching close to or above toxic levels in some locations.

Stripping polarography and the reduction of copper(II) in sea water at the hanging mercury drop electrode

Abstract An approximate but general theoretical treatment for reversible and irreversible stripping polarographic systems is presented. The treatment is based on the development of an average current (i), which at plating times exceeding 15 s. is analogous to the instantaneous current in d.c. polarography. Plots of i vs. (E – E°) are generated for reversible and irreversible waves and are discussed for the reduction of copper(II) in sea water as an example. From stripping polarography and anodic stripping voltammetry, this work indicates that the overall reduction of copper(II) at the natural pH is kinetically hindered and thus is “irreversible”. The reversibility and the determination of copper in sea water by a.s.v. can be improved by acidification and/or by the addition of ethylenediamine.

The Influence of Diffusion Fluxes on the Detection Limit of the Jalpaite Copper Ion-Selective Electrode

Abstract : It has been suggested that electrode dissolution and the concomitant saturation of the electrodes diffusion layer restricts the detection limit of the jalpaite Cu ion-selective electrode (ISE) to samples with total Cu levels above 10(exp-5) mol dm(exp -3) [1, 2]. This article will use rotating disk electrode (RDE) data for San Diego Bay seawater and Ficks law of diffusion to demonstrate that the static commercial Orion Cu ISE (employing a jalpaite membrane) produces a background level of contamination of (2.0 plus or minus 0.5) x 10(exp -8) mol dm(exp -3) total Cu, and the reduced thickness of the Orion Cu ISEs diffusion layer in the presence of hydrodynamic flow [e.g., at an RDE, or in continuous flow analysis (CFA)] lowers the background contamination of Cu to < 10(exp-9) mol dm(exp -3). Furthermore, the RDE Cu ISE employing an electrode fabricated using jalpaite precipitated in 80% excess Na2S, so as to minimize the presence of occluded and leachable Cu salts and extraneous phases such as silver sulfide [3 - 5], reveals an improvement in the lower limit of detection compared to the commercial Orion Cu ISE.

Studies of cadmium—ethylenediamine complex formation in seawater by computer-assisted stripping polarography

Abstract An equation for stripping polarographyis derived,relating the half-wave potential (E* 1 2 ), ligand concentration, and dissociation constant of a complexed metal ion. This equation is similar to that for classical polarography, but contains an additional term which makes (E* 1 2 ) a linear function of the logarithm of the time. A computer-assisted system for generating stripping polarographic curves is also described. This system is used to characterize 10-8 M cadmium in a potassium nitrate solution and in sea water.

High-resolution determination of the pH of seawater with a flow-through system

Abstract Highly resolved, precise, underway pH measurements have been made by property configuring a pH measurement “system”. The system consists of pH and temperature sensors mounted in a flow-through manifold, with the analog signals recorded by a data acquisition unit. Temperature is monitored rather than controlled during the measurements. pH is computed from electrode potential by knowing the temperature characteristics of the electrode in both seawater and in two seawater buffers. With this system, fine pH structure (

Effects of Dissolved and Complexed Copper on Heterotrophic Bacterial Production in San Diego Bay

Bacterial abundance and production, free (uncomplexed) copper ion concentration, total dissolved copper concentration, dissolved organic carbon (DOC), total suspended solids (TSS), and chlorophyll a were measured over the course of 1 year in a series of 27 sample “Boxes” established within San Diego Bay. Water was collected through a trace metal-clean system so that each Box’s sample was a composite of all the surface water in that Box. Bacterial production, chlorophyll a, TSS, DOC, and dissolved copper all generally increased from Box 1 at the mouth of the Bay to Box 27 in the South or back Bay. Free copper ion concentration generally decreased from Box 1 to Box 27 presumably due to increasing complexation capacity within natural waters. Based on correlations between TSS, chlorophyll a, bacterial production or DOC and the ratio of dissolved to free Cu ion, both DOC and particulate (bacteria and algae) fractions were potentially responsible for copper complexation, each at different times of the year. CuCl2 was added to bacterial production assays from 0 to 10 μg L−1 to assess acute copper toxicity to the natural microbial assemblage. Interestingly, copper toxicity appeared to increase with decreases in free copper from the mouth of the Bay to the back Bay. This contrasts the free-ion activity model in which higher complexation capacity should afford greater copper protection. When cell-specific growth rates were calculated, faster growing bacteria (i.e. toward the back Bay) appeared to be more susceptible to free copper toxicity. The protecting effect of natural dissolved organic material (DOM) concentrated by tangential flow ultrafiltration (>1 kDa), illite and kaolinite minerals, and glutathione (a metal chelator excreted by algae under copper stress) was assessed in bacterial production assays. Only DOM concentrate offered any significant protection to bacterial production under increased copper concentrations. Although the potential copper protecting agents were allowed to interact with added copper before natural bacteria were added to production assays, there may be a temporal dose–response relationship that accounts for higher toxicity in short production assays. Regardless, it appears that effective natural complexation of copper in the back portions of San Diego Bay limits exposure of native bacterial assemblages to free copper ion, resulting in higher bacterial production.