The use of membrane electrodes in the determination of sulphides in sea water

The direct potentiometric determination of sulphides in natural sea water with a sulphide-selective membrane electrode is proposed. The experimental evaluation of the “apparent mixed” dissociation constants and the thermodynamic activity coefficient in spiked sea water samples, by means of the electrode, permits direct calibration in terms of activity. Alternatively, it is possible to establish, for natural sea water, an experimental equation for the correction of the electrode potentials in terms of pH; this allows direct calibration of the electrodes in terms of total sulphide concentration. This criterion can be applied to any aqueous solution.     

Anodic stripping voltammetry with the florence mercury film electrode. determination of copper,lead and cadmium in sea water

The use of the rotating glassy carbon electrode mercury plated in situ for anodic stripping voltammetry has been investigated. The choice of electrode material is discussed. The effect of instrumental parameters on the stripping response for copper, lead and cadmium in sea water is studied, the results being in accordance with the theory of thin film electrodes. The variation in the observed sensitivity for the three metals in sea water is discussed in terms of complex-forming ligands. Lastly the performance of the film electrode is compared to that of the hanging mercury drop electrode.     

The determination of zinc,cadmium, lead and copper in a single sea-water sample by differential pulse anodic stripping voltammetry

A comparative study is described of the anodic stripping voltammetry of sea water at its natural pH and at acetate-buffered pH, with a mercury film electrode. The reproducibility of the oxidation current peaks for copper and lead is improved and the electrode memory effect decreases, when the sample is acetate-buffered (pH 5.8). Determinations of zinc at the natural pH of sea water are inaccurate, because of the formation of Zn—Cu and Zn—Ni intermetallic compounds in the mercury film. The formation of such compounds can be prevented by the addition of gallium ions to acetate-buffered samples. A procedure for the determination of Cu, Pb, Cd and Zn in sea water is described.     

The determination of platinum in sea water by adsorptive cathodic stripping voltammetry

The catalytic effect of the formazone complex with platinum on the development of hydrogen at a mercury electrode is used to provide a very sensitive method of determining dissolved platinum in fresh and sea water by adsorptive cathodic stripping voltammetry. The optimal analytical conditions include the addition of 0.012% (w/v) formaldehyde, 0.0015% (w/v) hydrazine and 0.5 M sulphuric acid to the sea water. The complex is adsorbed for 1–20 min at ?0.925 V on the hanging mercury drop electrode, followed by a differential-pulse scan in a negative direction. The hydrogen reduction peak catalysed by the platinum complex appears at ?1.045 V. The limit of detection is 0.04 pM Pt with an adsorption time of 10 min, which is quite sufficient to determine dissolved platinum in sea water. The interference of surface-active compounds is eliminated by ultraviolet irradiation of the acidified sample. The method is applied to several sea-water samples. Comparative experiments showed that stripping chronopotentiometry is not sufficiently sensitive to determine platinum in sea water without preconcentration.     

Salinity measurements with polyaniline matrix coated wire electrodes

Potentiometric measurements were carried out with a wire electrode coated with a mixture of polyaniline and polystyrene. The salinity in water is obtained by measuring the potential difference between the coated wire electrode and an Ag|AgCl, saturated KCl reference electrode. The salinity of a sample is obtained by the interpolation of its potential in the calibration curve obtained with KCl solutions of known concentrations. The results indicated that it is possible to measure the salinity in sea water, brackish water and drinking water in the range of 0.010 to 75‰.     

An alternative approach to selective sea water oxidation for hydrogen production

Sea water electrolysis is one of the promising ways to produce hydrogen since it is available in plentiful supply on the earth. However, in sea water electrolysis toxic chlorine evolution is the preferred reaction over oxygen evolution at the anode. In this work, research has been focused on the development of electrode materials with a high selectivity for oxygen evolution over chlorine evolution. Selective oxidation in sea water electrolysis has been demonstrated by using a cation-selective polymer. We have used a perm-selective membrane (Nafion^®), which electrostatically repels chloride ions (Cl⁻) to the electrode surface and thereby enhances oxygen evolution at the anode. The efficiency and behaviour of the electrode have been characterized by means of anode current efficiency and polarization studies. The surface morphology of the electrode has been characterized by using a scanning electron microscope (SEM). The results suggest that nearly 100% oxygen evolution efficiency could be achieved when using an IrO₂/Ti electrode surface-modified by a perm-selective polymer.     

A Polyoxometalate-Based Binder-Free Capacitive Deionization Electrode for Highly Efficient Sea Water Desalination

Capacitive deionization is a promising technique in sea water desalination. Compared with common electrodes, mixed capacitive-deionization electrodes exhibit better performance in sea water desalination because they integrate pseudocapacitance and electric double-layer capacitance in one system. Herein, a 3D binder-free mixed capacitive-deionization electrode was fabricated by direct electrodeposition of SiW₁₂O₄₀⁴⁻ and polyaniline on a 3D exfoliated graphite carrier. In this electrode, SiW₁₂O₄₀⁴⁻/polyaniline composite particles with a size of about 100–120 nm are dispersed homogenously on the 3D exfoliated graphite carrier. Its specific capacitance reaches 352 F g⁻¹ at 1 A g⁻¹. With increasing current from 1 to 20 A g⁻¹, the specific capacitance only decays by 32 %. When employed in sea water desalination, the performance of this mixed capacitive-deionization electrode is also excellent. At 1.2 V, the salt adsorption capacity of this mixed electrode reaches 23.1 mg g⁻¹ with a salt adsorption rate of 1.38 mg g⁻¹ min⁻¹ in 500 mg L⁻¹ NaCl. The performance of this electrode is well retained after 30 cycles. The excellent sea water desalination performance originates from the synergistic effect between SiW₁₂O₄₀⁴⁻ and polyaniline. This work has developed polyoxometalate as a new material for capacitive-deionization electrodes.     

Atomic-absorption spectrometric determination of cadmium,lead and zinc in salts or salt solutions by hanging mercury drop electrodeposition and atomization in a graphite furnace

Atomic absorption spectrometric methods are described for the determination of trace amounts of cadmium, lead and zinc in salts or salt solutions. The metals are separated from the salt matrix by electrolysis on a hanging mercury drop electrode, the mercury is transferred to a graphite boat and removed by evaporation, and the metals are determined by atomization. The feasibility of the technique was tested by analysis of sea water and of reagent-grade potassium chloride. For comparison the three metals were also determined in the sea water by stripping voltammetry, good agreement being found.     

极谱催化波二阶导数卷积伏安法测定痕量钼

用极谱催化波测钼(Ⅵ)有较高灵敏度。本文研究把卷积伏安法应用于钼(Ⅵ)的催化波测定。     

Direct determination of bismuth and antimony in sea water by anodic stripping voltammetry

A method based on anodic stripping voltammetry at the mercury-coated graphite electrode has been developed for the direct determination of bismuth and antimony at their natural levels in sea water. Bismuth plated at -0.4 V from sea water made 1 M in hydrochloric acid gives a stripping peak proportional to concentration at -0.2 V without interference from antimony or other metals normally present. Antimony may be plated from sea water made 4 M in hydrochloric acid and gives a stripping peak at -0.2 V proportional to the sum of bismuth and antimony. By use of the standard addition technique, satisfactory results were obtained for sea water samples with concentration ranges of 0.02–0.09 μg kg^?1 for bismuth and 0.2–0.5 μg kg^?1 for antimony.     

Preconcentration of Cr(III) and total Cr in waters for flame AAS in a flow-through electrochemical/sorption cell

Chromium in water samples is determined by flame atomic absorption spectrometry (AAS) after the preconcentration of Cr(III) species on activated alumina at pH 7 in a flow system coupled on-line to the AAS instrument. The total Cr concentration is determined after the electrochemical reduction of chromate ions to Cr(III) which are preconcentrated together with the original Cr(III) species in the sample. Both the reduction and the sorption are carried out in a combined cell containing a porous electrode, a layer of the sorbent and the counter electrode in series. The porous electrode is made of glassy carbon particles coated with gold. Tap, river and synthetic sea water samples were analyzed with this method. The detection limits are 0.5 ng/ml and 250 ng/ml for 500 ml and 1 ml sample solution, respectively.     

Preconcentration of Cr(III) and total Cr in waters for flame AAS in a flow-through electrochemical/sorption cell

Chromium in water samples is determined by flame atomic absorption spectrometry (AAS) after the preconcentration of Cr(III) species on activated alumina at pH 7 in a flow system coupled on-line to the AAS instrument. The total Cr concentration is determined after the electrochemical reduction of chromate ions to Cr(III) which are preconcentrated together with the original Cr(III) species in the sample. Both the reduction and the sorption are carried out in a combined cell containing a porous electrode, a layer of the sorbent and the counter electrode in series. The porous electrode is made of glassy carbon particles coated with gold. Tap, river and synthetic sea water samples were analyzed with this method. The detection limits are 0.5 ng/ml and 250 ng/ml for 500 ml and 1 ml sample solution, respectively.     

Integral toxicity test of sea waters by an algal biosensor

An integral toxicity test, based on an algal biosensor and suitable to be used in sea water, is presented. The biosensor was designed and built by coupling a Clark oxygen electrode as transducer and the marine alga Spirulina subsalsa as biological mediator; it constitutes the "core" in a lab-scale prototype of a flow apparatus suitable to continuously monitor, in sea water, the photosynthetic activity of the alga and, from its variation, the marine pollution from the toxicological point of view. Inorganic pollutants (heavy metals) were tested in previous researches while organic ones (chlorophenols, pesticides and surfactants) are the object of the present paper.     

离子色谱法检测海水中常见阴离子的前处理法研究——电解银电极法

提出一种采用电解银电极降低海水中大量Cl 的浓度的前处理法 ,以便海水中微量的Br ,NO3 以及SO4 2 可以采用快速、灵敏的离子色谱法检测 .该前处理方法简单 ,快速 ,所测量的离子回收率均在 95%以上     

In situ electrodeposition for the determination of lead and cadmium in sea water

Electrodeposition techniques for the direct determination of lead and cadmium in sea water at the natural pH and in the presence of dissolved oxygen are examined. Anodic stripping voltammetry, at either the hanging mercury drop electrode or glassy carbon thin film electrode, is suitable for the determination of labile lead and cadmium. The presence of dissolved oxygen increases the height of the lead wave with a shift to more negative potentials. A more versatile technique is in situ deposition of labile metals on a mercury-coated graphite tube electrode. The mercury film, deposited in the laboratory, is stable on the dried tubes which are used later for field electrodeposition. The deposited metals are determined by electrothermal atomic absorption spectrometry.     

Determination of heavy metals in real samples by anodic stripping voltammetry with mercury microelectrodes : Part 2. Application to Rain and Sea Waters

Differential-pulse anodic stripping voltammetry at a mercury microelectrode is applied to determine labile and total zinc, cadmium, lead and copper in samples of rain and sea water. The low ohmic drop associated with microelectrodes permits reliable measurements in rain water without addition of supporting electrolyte. The values found in a typical sample were 0.95 μg l^?1 Cu, 0.38 μg l^?1 Pb, 0.01 μg l^?1 Cd and 0.95 μg l^?1 Zn, with relative standard deviations in the range 4–18%. The small effects of organic matter at microelectrodes, compared with those at a hanging mercury drop electrode, allow sensitive and reliable measurements of labile metals in surface sea water. Total metal concentrations are determined after acidification to pH 1.5 with hydrochloric acid. The results are compared with those obtained with atomic absorption spectrometry and with differential-pulse anodic stripping voltammetry at conventional mercury electrodes. Satisfactory results were obtained for a reference sea water.     

Staircase voltammetry as a rapid detection method for anodic stripping determination of lead

Rapid-scan staircase voltammetry is used to strip lead plated on a rotating mercury film electrode. With potential steps of 10 mV every 64 μs, the entire stripping of the metals is made in only 4 ms. Noise is reduced by averaging several current measurements on each step. The method allows quantification of 0.1 μg l^?1 lead within a total time to less than 4 min. Because of the rapid scan, the rotation of the electrode can continue during the stripping step. Oxygen does not affect the measurements although a small decrease in current is observed. The method is tested on a sample of sea water. Some results are also given for cadmium.     

Measurements of trace concentrations of mercury in sea water by stripping chronopotentiometry with gold disk electrode: influence of copper

A stripping chronopotentiometric method, using a rotating gold disk electrode for mercury measurements in sea water is described. Compared with a same method using a stationary gold film electrode, this method has a eight times higher sensitivity and a detection limit of 5 ng l⁻¹ after 10 min deposition time. Moreover, the time needed for gold plating is eliminated. Compared with other electrochemical methods capable of measuring mercury at low concentrations, the present method is more simplified with no degassing step and no need to use a medium-exchange procedure before the stripping step. These characteristics render the method easily practicable on board oceanographic vessels for ‘in situ’ measurements.     

A method for characterization of sea surface microlayer based on monolayer properties in presence and absence of phospholipids

Electrochemical impedance spectroscopy, ac voltammetry and fractal analysis were used to characterize model compounds, compound mixtures and extracted samples of sea surface microlayer (ssm) und underlying water (ulw). The reasons for carrying out this work were to use the scientific basis of these characterizations in future on-line analytical procedures of ssm. The mercury (Hg) drop electrode uncoated and coated with a monolayer of dioleoyl phosphatidylcholine (DOPC) was used as an experimental basis for investigation of the major sea surface film forming material. Firstly, the interaction of the uncoated and DOPC coated Hg electrode with model water insoluble compounds of increasing polarity was investigated. The compounds studied in order of increasing polarity were: nonadecane, stearic acid, cholesterol and cardiolipin. Subsequently the electrochemical response of the system to different ssm extracts was compared to signals observed with model compounds to demonstrate method selectivity. From the electrochemical results, it is observed that both the molecular structure and polarity of the investigated compounds have a role in their interaction with the uncoated and DOPC coated electrode. In the fractal analysis the increase above 2 of fractal dimension D imparted to the DOPC layer is related to the degree of apolarity of the additive model compound. Consistent with this, the more apolar hexane extracted ssm 2 imparts a fractal dimension D value of 2.45 when incorporated in DOPC layers. The electrochemical response to the ssm and ulw follows that characteristic of sterol compounds.     

A battery-powered,computerized instrument for the field-based determination of fluoride by the ion-selective electrode technique

Battery-powered complementary metal-oxide semiconductor (CMOS) electronic devices are used to develop computerized instrumentation based on an ion-selective electrode for environmental monitoring in the field. The development of CMOS-based instrumentation for the determination of fluoride in drinking water, river water, lake water and sea water is described. The instrument is portable and completely field-programmable. Under software control, the equilibrium potential and fluoride concentration, based on a double standard-addition method, are calculated. The associated temperature, date and time form part of the data-logging record. Data obtained in the field are shown to compare satisfactorily with those obtained on samples which were stored and returned to the laboratory for examination by conventional mains-powered instrumentation. Accuracy is good and precision is only slightly poorer than that of mains-powered laboratory instrumentation.