Cobalt In Seawater Research Articles

Determination of Cobalt in Seawater Using Neutron Activation Analysis after Preconcentration by Adsorption ontoγ-MnO2Nanomaterial

Theγ-MnO2nanomaterial has been used to adsorb cobalt in the seawater at Phan Thiet City, Binh Thuan Province, Vietnam. Its concentration is determined by using the neutron activation analysis (NAA) method at the Dalat nuclear research reactor. Factors affecting the uptake of cobalt on theγ-MnO2material such as the pH, adsorption time, and initial cobalt(II) concentration are investigated. The irradiated experiment data are calculated using the K0-Dalat program. The results obtained show that the trace dissolved cobalt in Phan Thiet seawater is found equal to 0.25 ± 0.04 μg/L (n=5,P=95%) with the adsorption efficiency being higher than 95% (n=4,P=95%).

Determination of total dissolved cobalt in UV‐irradiated seawater using flow injection with chemiluminescence detection

A sensitive flow‐injection method with chemiluminescence detection (FI‐CL) for the determination of dissolved cobalt in open ocean samples, suitable for shipboard use has been developed. To date, FI methods for dissolved cobalt have been used only in coastal and estuarine waters. Therefore, significant modifications to existing methods were required, including (1) the use of a commercially available iminodiacetate (IDA) resin (Toyopearl AF‐chelate 650M) in place of resin immobilized 8‐hydroxyquinoline for online preconcentration and matrix removal, (2) the introduction of acidified ammonium acetate (pH 4) as a column‐conditioning step before sample loading and rinse steps, and most importantly, (3) UV irradiation of acidified seawater samples to determine total dissolved cobalt, rather than an operationally defined fraction. This method had a detection limit of 4.5 pM (3σ of the blank). The accuracy of the method was evaluated by determining total dissolved cobalt in acidified North Pacific deep seawater (1000 m) samples from the Sampling and Analysis of Iron (SAFe) program and NASS‐5. The method yields a mean (± SD) value of 40.9 ± 2.6 pM (n = 9), which is in excellent agreement with the SAFe consensus value of 43 ± 4 pM, and 208 ± 30 pM for NASS‐5 (certified value 187 ± 51 pM). This study demonstrates that UV irradiation is an essential step for the determination of total dissolved cobalt in seawater by FI‐CL. The method was applied to vertical profiles from the Sargasso Sea, indicating that total dissolved cobalt is influenced by both biological and physical processes.

Changes in mobility and solubility of the redox sensitive metals Fe, Mn and Co at the seawater-sediment interface following CO<sub>2</sub> seepage

Abstract. The impact of CO2 seepage on the solubility and distribution of the redox-sensitive metals iron, manganese, and cobalt in seawater and sediment pore water has been studied in experiments in laboratory-scale 0.6 m3 chambers. The mobility and solubility of Fe, Mn and Co were investigated in seawater, membrane filtered seawater, and DGT samplers deployed in water and sediment during a 26 day CO2 seepage study. During the first phase of the experiment of CO2 seepage (0–16 days), total acid-leachable (pH 1) and "dissolved" (<0.2 μm) concentrations of Fe, Mn and Co (DFe, DMn and DCo) in the seawater increased significantly; the ratios of concentrations of DFe, DMn and DCo in the CO2 chamber to the corresponding values in the control chamber (RDFe, RDMn and RDCo) were as high as 6, 65 and 58, respectively. The second phase of experiment consisted of an additional 10 days of incubation, where the concentrations of all the metals studied still increased but at reduced rates for DMn and DCo. The highest values of RDFe, RDMn and RDCo were about 3 for all metals during this part of the experiment. DGT (diffusive gradients in thin film) labile fractions denoted FeDGT, MnDGT and CoDGT were, respectively 50, 25 and 22 times higher in the CO2 seepage chamber than in the control chamber in the first phase of the experiment. During the second phase, all DGT labile metal concentrations still increased considerably, most notably for Fe. The ratio of FeDGT in the CO2 chamber to that in the control (RDGT-Fe) was still high, about 5, in the second phase of the experiment, whereas the increase in MnDGT and CoDGT slowed down. Our results indicate that acidification following CO2 seepage enhances the mobility and solubility of Fe Mn and Co in sediment and overlying water with contribution of changing in redox conditions and seepage related re-suspension.

Determination of organic complexation of cobalt in seawater by cathodic stripping voltammetry

A method was developed to determine the extent of cobalt complexation with organic ligands in seawater, and applied to samples from the North Eastern Atlantic Ocean. The cobalt speciation was determined using catalytic cathodic stripping voltammetry with ligand competition against the adsorptive ligand (nioxime). Optimised conditions include a nioxime concentration of 200 nM, 0.07 M ammonia/ammonium chloride pH buffer (pH 9.1), and 0.5 M nitrite. The stability of the mixed complex of cobalt, nioxime and ammonia was calibrated against EDTA. The cobalt speciation in the open-ocean surface waters was found to be dominated by complexation to natural organic ligands with conditional stability constants (log KCoL′) ranging between 15.6 and 16.1 and with ligand concentrations between 22 and 60 pM. The cobalt concentrations varied between 25 pM in the open-ocean waters and 103 pM in the English Channel, and were less than the ligand concentrations in many of the surface oceanic waters. The ligand concentration at depths between 30 and 115 m (average 22 pM) was lower than that of cobalt, whereas at other depths (shallower as well as deeper), the ligand concentrations were between 26 and 31 pM, sometimes greater than the cobalt concentrations. The cobalt and ligand concentrations in these waters are finely balanced, strongly binding all cobalt when the ligands are in excess. Free Co2+ concentrations calculated for the open-ocean surface waters are extremely low (<5 fM) which could cause cobalt limitation to certain phytoplankton such as coccolithophores and cyanobacteria if the organic complexes are unavailable. If this organic complexation of cobalt occurs also in other regions characterised by low cobalt concentrations, iron-limited waters in high-nitrate low-chlorophyll regions may be cobalt-limited too.

Determination of ultra-trace amounts of cobalt in seawater by graphite furnace atomic absorption spectrometry after pre-concentration with Ni/8-quinolinol/1-nitroso-2-naphthol complex

A sensitive and accurate method for the determination of ultra-trace amounts of cobalt in seawater is described. Ultra-trace amounts of cobalt were pre-concentrated by co-precipitation with a combination of 8-quinolinol and nickel as a carrier element and 1-nitroso-2-naphtol as an auxiliary complexing agent. The co-precipitates obtained were directly measured by graphite furnace atomic absorption spectrometry using the solid-sampling technique. The co-precipitation conditions for ultra-trace amounts of cobalt with Ni/8-quinolinol/1-nitroso-2-naphtol complex were investigated in detail. It was found that ultra-trace amounts of cobalt are co-precipitated quantitatively with Ni/8-quinolinol/1-nitroso-2-naphtol complex in the pH range of 5.5–8.5. The concentration factor by the co-precipitation reached about 33,000-fold for 1000 ml of the aqueous sample. The proposed method has been successfully applied to the determination of ultra-trace amounts of cobalt in seawater, and the detection limit for cobalt which was defined as the concentration calculated from three times of the standard deviation of the procedural blanks, is 1 ng/l for 1000 ml portions of seawater samples.

Sequential flow analysis coupled with ACSV for on-line monitoring of cobalt in the marine environment

The development of a compact instrument for on-line measurement of trace metals in seawater is described. The system is based on adsorptive cathodic stripping voltammetry (ACSV), and on the concept of sequential flow analysis, to perform on-line measurements with controlled perturbation of natural equilibria of the element. The design combines a low volume flow cell with a miniature solenoid pump and valves to achieve low power consumption. The flow segmentation is time-controlled and the detection step takes place in a well-defined part of the flow stream where reagent and sample occur mixed. The system was tested on the determination of cobalt in seawater but it is likely that the same technique can be used to determine other metals detectable by CSV. The determination range was 6–1050 pmol/L cobalt with a detection limit (3σ) of 6 pmol/L. The measurement rate was about 60 h–1. Comparative measurements were carried out using continuous flow analysis. The apparatus was used continuously on board a ship to determine the distribution pattern of cobalt in surface waters off the coast of California.

Determination of Cobalt in Seawater by Catalytic Adsorptive Cathodic Stripping Voltammetry

A new procedure for the direct determination of picomolar levels of cobalt in seawater is presented. Cathodic stripping voltammetry is preceded by adsorptive accumulation of the cobalt-nioxime (cyclohexane-1,2-dione dioxime) complex from seawater containing 6 μM nioxime and 80 mM ammonia at pH 9.1, onto a hanging mercury drop electrode, followed by reduction of the adsorbed species. The reduction current is catalytically enhanced by the presence of 0.5 M nitrite. Optimized conditions for cobalt include a 30 s adsorption period at -0.7 V and a voltammetric scan using differential pulse modulation. According to the proposed reaction mechanism, dissolved Co(II) is oxidized to Co(III) upon addition of nioxime and high concentrations of ammonia and nitrite; a mixed Co(III)-ammonia-nitrite complex is adsorbed on the electrode surface; the Co(III) is reduced to Co(II) (complexed by nioxime) during the voltammetric scan, followed by its chemical reoxidation by the nitrite, initiating a catalytically enhanced current. A detection limit of 3 pM cobalt (at an adsorption period of 60 s) enables the detection of this metal in uncontaminated seawater using a very short adsorption time. UV digestion of seawater is essential, as part of the cobalt may occur strongly complexed by organic matter and rendered nonlabile. The method was applied successfully to the determination of the distribution of cobalt in the water column of the Mediterranean.

On-line column preconcentration for the determination of cobalt in sea water by flow-injection chemiluminescence detection.

A flow-injection method for the determination of dissolved cobalt(II) in sea water has been studied based on a combination of column preconcentration using 8-quinolinol immobilized on silica gel, fluoride containing metal alkoxide glass (8HQ-MAF) and chemiluminescence detection with a gallic acid-hydrogen peroxide system. Co(II) is selectively recovered from an acidified sample with 8-quinolinol immobilized on silica gel. After elution with dilute hydrochloric acid the resultant eluent is mixed with the reagent solutions, heated to 60 ( degrees )C and then introduced into the CL cell. The analysis time including the 2-min sample load was 8 min per sea water sample with a corresponding detection limit of 0.62 ng l(-1) (3sigma). The average standard deviation calculated for 10 replicate measurements of artificial sea water samples with a concentration of 10 ng l(-1) cobalt was +/-2.1%. The method has been tested with the standard reference sea waters NASS and CASS.

Shipboard determination of dissolved cobalt in sea-water using flow injection with catalytic spectrophotometric detection

A flow injection spectrophotometric technique for the determination of cobalt in sea-water and hydrothermal sea-water solutions is described. It is based on the catalytic effect of cobalt(II) on the oxidation of N,N′-diethyl-p-phenylenediamine by hydrogen peroxide in the presence of Tiron as an activator. The catalytic activity of cobalt(II) was found to be significantly enhanced by the presence of sea-water matrix components, especially calcium ions, improving the sensitivity of cobalt determination in sea-water. The comparatively weak basic medium (pH 8.7–9.0) of the reaction and its relative freedom from co-existing ions allowed the direct analysis of sea-water to be conducted effectively without any preliminary steps. The sampling rate was 50 h–1. The limit of detection for cobalt was 1 ng l–1 and the relative standard deviation at the level of 10–100 ng l–1 was 2–8%(n= 5). The technique was confirmed to be accurate on the basis of the analysis of the standard sea-water solutions CASS-2 and NASS-2. Artificial hydrothermal solution samples were analysed by the proposed technique and the results were in good agreement with data obtained by ICP-MS.

Determination of nickel and cobalt in wastewaters and seawater by constant current stripping potentiometry with nitrite enhancement of the stripping signal

AbstractA rapid and highly sensitive method using constant current stripping potentiometry for the determination of nickel and cobalt in seawaters and industrial wastewaters has been established. The method is based on the adsorptive accumulation of nickel and cobalt in the presence of either dimethylglyoxime (DMG) or α‐benzyldioxime (α‐BD) prior to stripping using a constant reducing current. Nitrite is used in the stripping step for the catalytic enhancement of the stripping signal. Analytical protocols for standard solutions using DMG or α‐BD show good precision (RSD's between 3 and 4% on the same film) and detection limits (30 ng/L for Ni/DMG; 10‐ng/L for Co/DMG; 9ng/L for Co/α‐BD). However, iron interferes significantly with the determination of cobalt using α‐BD. With DMG, the simultaneous determination of nickel and cobalt is possible and has been developed into a protocol readily applicable to the routine determination of these metals. The analytical protocol is rapid, easy to perform and the results are in agreement with those obtained by graphite furnace atomic absorption spectrophotometry. The DMG procedure has also been optimized for the determination of cobalt alone, which has advantages for determinations at concentrations of 1 μg/L or less.

High‐Performance adsorptive cathodic stripping voltammetry of nickel and cobalt in seawater

AbstractThe voltammetric determination of trace metals in seawater suffers from the interference of dissolved oxygen and engine vibrations onboard ship. It is here attempted to overcome these interferences using a high‐frequency (1 to 20 kHz) staircase modulation during the voltammetric scan (high‐performance adsorptive cathodic stripping voltammetry, HPACSV). Comparative experiments using the square‐wave modulation showed that this modulation was not effective at such a high frequency. A comparison between various complexing agents (DMG and nioxime) and pH buffers (HEPES/NH4OH, borate/NaOH, and TEA/NH4OH) showed that the determination of nickel and cobalt was similarly improved by the high‐speed potential scan in all conditions. Fast potential scans cause a large increase of the peak area and peak heights using staircase modulation. The peaks are wider, and the peak potentials are shifted toward negative values due to the ohmic drop, but the analytical determination is not disturbed. Optimal sensitivity for the determination of cobalt and nickel in seawater was obtained using TEA buffer and DMG as the adsorptive ligand. The nioxime wave was found to interfere in the cobalt peak at high scan rates so that this ligand is not recommended for HPACSV. Comparative tests showed that the sensitivity for nickel and cobalt determinations was highly improved by the fast scan rates. Furthermore, the reduction current of dissolved oxygen was partially masked so that measurements could be taken without a previous purge of the sample. Finally, the scans were insensitive to the solution turbulence so measurements could be readily carried out onboard of an oceanographic vessel or without switching off the stirrer. Low levels of nickel (2 nM) could be determined in seawater by using a deposition time of 20 seconds and of 120 seconds for 0.05 nM cobalt from turbulent and unpurged solutions. A fast determination method for labile nickel and cobalt is proposed.

Determination of ultra-trace amounts of cobalt in ocean water by laser-excited atomic fluorescence spectrometry in a graphite electrothermal atomizer with semi on-line flow injection preconcentration

A method has been developed for the determination of trace and ultra-trace amounts of cobalt in sea-water. Samples of CASS-2 Nearshore Seawater and NASS-4 Open Ocean Water reference materials from the National Research Council of Canada were employed. Laser-excited atomic fluorescence spectrometry in an electrothermal atomizer (ET-LEAFS) was used, and integrated with semi on-line flow injection microcolumn preconcentration. For cobalt, the effects of pH on the preconcentration efficiency, the concentration of the chelating agent and the distribution of cobalt in the ethanol eluate were studied. A bonded silica, with octadecyl functional groups (C18) in a 10 µl column, was employed for preconcentration of cobalt in ocean water. Ocean water volumes of 0.40 and 1.00 ml were required for the determination of cobalt in CASS-2 and NASS-4, respectively. These volumes were almost two orders of magnitude smaller than those required by inductively coupled plasma mass spectrometry and some other competitive techniques. The preconcentration factors were 5- and 12.5-fold for CASS-2 and NASS-4, respectively. The detection limits (3s), based on 12.5-fold preconcentration, were 0.08 and 1.0 ng l–1 for cobalt in aqueous standard solutions and in Ocean Water Reference Materials, respectively. Results for the determination of cobalt in CASS-2 and NASS-4 showed that there were no significant differences between the certified values and the measured values, based on Student's t-test at the 95% confidence level. The relative standard deviations for the determinations of the concentrations of cobalt in CASS-2 and NASS-4 were 9 and 13%, respectively.

The speciation of cobalt in seawater and fresh waters at 25.DEG.C..

The speciation of cobalt in seawater and fresh waters at 25.DEG.C..

Flow injection on-line separation and preconcentration for electrothermal atomic absorption spectrometry. Part 2. Determination of ultra-trace amounts of cobalt in water

Ultra-trace amounts of cobalt in sea-water were determined by flow injection on-line sorbent extraction–preconcentration coupled with electrothermal atomic absorption spectrometry. With sodium diethyldithiocarbamate as the complexing agent and C18-bonded silica reversed-phase sorbent as the column material, a 42-fold enhancement of peak area, compared with that for direct 40 µl sample introduction, was obtained with a 120 s preconcentration and 5.6 ml of sample. The atomization signal was directly proportional to the preconcentration time. An enhancement factor of 210 and a detection limit of 1.7 ng l–1 could be achieved with a 10 min sample loading time (28 ml). Hence, the extremely low cobalt concentration of 4.0 ng l–1 in National Research Council of Canada certified reference material NASS-1 Open Ocean Seawater could be determined within 12 min. Results obtained for sea-water and estuarine water certified reference materials agreed with the certified values with a relative standard deviation of 5.0%.

Determination of picomolar levels of cobalt in seawater by flow injection analysis with chemiluminescence detection

Flow injection analysis (FIA) was used to automate the determination of cobalt in seawater by the Co-enhanced chemiluminescent oxidation of gallic acid in alkaline hydrogen peroxide. A preconcentration/separation step in the FIA manifold with an in-line column of immobilized 8-hydroxyquinoline was included to separate the Co from alkaline-earth ions. One sample analysis takes 8 min, including the 4-min sample load period. The detection limit is approximately 8 pM. The average standard deviation of replicate analyses at sea of 80 samples was +/- 5%. The method was tested and intercalibrated on samples collected off the California coast.

Selective concentration of cobalt in seawater by complexation with various ligands and sorption on macroporous resins

Selective concentration of trace amounts of cobalt in seawater was examined by use of 14 ligands and 2 XAD resins. Complexed cobalt was collected after passage through a small XAD resin packed column. Complexes of coexisting metals were eluted with acidic solution. Cobalt complex was then eluted with a methanol-chloroform mixture. When ligands insoluble in water were used, the recovery of cobalt was not quantitative because of coprecipitation of the complex on the precipitated ligands. The combination of TAR, which forms a water-soluble inert complex with cobalt, and XAD-4 resin was preferable for the selective concentration of cobalt in seawater. This method was applied to the preconcentration of cobalt dissolved in seawater at nanogram-per-liter levels.

Determination of cobalt in seawater by graphite furnace atomic absorption spectrometry after preconcentration with diethyldithiocarbamate extraction and vacuum evaporation of solvent.

A simple and effective preconcentration method of cobalt from seawater is described. Cobalt is extracted as the diethyldithiocarbamate into carbon tetrachloride, then the solvent is evaporated by a rotary evaporator. The element is determined by graphite furnace atomic absorption spectrometry after dissolution of the residue with nitric acid and hydrogen peroxide. By using this method, cobalt in seawater with levels of ng dm-3 range could be determined.

Uptake and excretion of cobalt by sea cucumber Stichopus japonicus and prawn Penaeus japonicus.

Radiocobalt tracer experiments were carried out to obtain further information on the biochemical behavior of this nuclide in sea cucumber and prawn. The biological half lives of 60Co (inorganic cobalt in sea water) were calculated at 73 days for sea cucumber and 24 days for prawn. The 60Co-binding constituents in the organs and tissues of these organisms were extracted with a Tris-acetate buffer solution and separated using gel filtration on Sephadex G-75. Although most radioactivity (86%) in the crude extraction of sea cucumber (without intestine)was found in a relatively high molecular weight fraction (more than 80000), that in prawn liver was observed in a low molecular weight fraction (less than 5000). From analysis for carbohydrates, a large portion of carbohydrates in the prawn liver was found in the high molecular fraction, however, the presence was observed in the low molecular weight fraction, too. Further characterization by electrophoresis showed that this fraction contained at least four 60Co-binding proteins or peptides and significant quantities of 60Co-binding carbohydrates. The biological role and detailed chemical nature of the components await further study.

Spectrophotometric determination of cobalt in sea water and brines by solvent extraction with 2,2'-dipyridyl-2'-pyridylhydrazone

Cobalt (⩾ 1 ppb) can be determined very selectively by extracting its 2,2'-dipyridyl-2-pyridylhydrazone complex into iso-amyl alcohol and back-extracting into dilute perchloric acid. For 500-ml samples of sea water the relative standard deviation is 5% for 2 ppb of cobalt. For brines (30 g NaCl l -1 ), cobalt can be determined down to 5 × 10 -7% (5 ppb).

Anion-exchange separation and spectrophotometric determination of cobalt in sea water

Traces of cobalt in sea water have been preconcentrated by anion-exchange from acidified sea water in the presence of thiocyanate. Cobalt adsorbed on the resin column is stripped by elution with 2 M perchloric acid. Accompanying iron is removed subsequently by anion-exchange from 6 M hydrochloric acid medium. Cobalt in the eluate is determined spectrophotometrically with 4-(2-pyridylazo)resorcinol in the presence of EDTA and potassium cyanide. The anion-exchange — PAR method allows to determine cobalt very selectively in sea as well as non-saline waters on a 2 l sample basis. The method gives a coefficient of variation of ca. 10% at a cobalt level of 0.1–0.2 Μg per liter.