Effect of model organic compounds on square-wave voltammetric stripping analysis at the Nafion/chelating agent mercury film electrodes

The effect of various organic compounds on the Nafion/chelating agent mercury film electrodes (NCAMFEs) in square-wave anodic-stripping voltammetry (SWASV) is explored. Two chelating agents used to prepare the NCAMFEs are dimethylglyoxime and 2,2'-bipyridyl. Triton X-100, sodium dodecyl sulfate, albumin, gelatin, starch, camphor, and humic acid are used as model organic compounds, while cadmium, lead, and copper are used as test metal ions. The NCAMFEs are considerably more resistant to organic interferences than the Nafion-coated mercury film electrode. The implications of these interferences for the reliability and feasibility of stripping measurements using the NCAMFEs in real samples are discussed. Results presented for untreated urine and natural water samples demonstrate the analytical utility of the NCAMFEs in SWASV.     

Anodic-stripping voltammetry of heavy metals in the presence of organic surfactants

The efficacy of fumed silica for removal of sorption interferences by organic surfactants in the anodic-stripping voltammetry of heavy metals is demonstrated. Appropriate addition of silica to the sample solution rapidly "purifies" it from interfering surfactants during the nitrogen purge step. Up to at least 6 ppm of gelatin, Triton X-100, albumin or Liqui-Nox then does not affect the stripping response of cadmium, lead and zinc at the hanging mercury drop electrode. A relative standard deviation of 5.5% is obtained for 20 successive measurements of 1 x 10(-7)M lead in the presence of 2 ppm Triton X-100. Analogous improvements are observed at the mercury film electrode (in the presence of up to 60 ppm of these surfactants). The use of silica thus possesses the advantages of speed, efficiency, simplicity and low cost compared to other schemes for dealing with surfactant interferences in anodic-stripping voltammetry.     

Optimization and comparison of four mercury working electrodes in speciation studies by differential-pulse anodic stripping voltammetry

Four types of working electrodes are compared with respect to sensitivity, resolution, peak width and suitability for copper speciation studies by differential-pulse anodic stripping voltammetry. The hanging mercury drop electrode, two rotating mercury film electrodes with in-situ and pre-formed films and a stationary mercury film electrode with a vibrationally induced jet-stream are examined. The last electrode appears to be the most useful system with the highest sensitivity. Conditions for mercury film formation must be optimized for each individual electrochemical system in order to avoid erroneous conclusions from standard addition procedures and apparent complexation capacity measurements.     

Determination of copper in seawater by anodic stripping voltammetry

Copper in surface seawater has been determined using both hanging mercury drop and thin film electrodes. Total copper was found to be in the range 0.4–0.7 μg l^?1, and labile copper in the range 0.2–0.4 μg l^?1. Most of the copper present in seawater is complexed with or adsorbed on organic matter, and a smaller percentage is associated with inorganic colloids. Seawater contains both organic and inorganic compounds which will react with approximately 1×10^?8M added ionic copper. Because of the presence of the complexing agents, peak current-copper concentration calibration curves in seawater are non-linear, and care must be exercised in using spiked results in the calculation of the copper content. The thin film electrode (TFE) is more suitable than the hanging mercury drop electrode for determining copper in seawater, although the TFE results are more dependent on deposition potential, and suffer from interference by nickel if very negative deposition potentials are used.     

Square-wave anodic stripping voltammetric determination of thallium(I) at a Nafion/mercury film modified electrode

A Nafion/mercury film electrode (NMFE) was used for the determination of trace thallium(I) in aqueous solutions. Thallium(I) was preconcentrated onto the NMFE from the sample solution containing 0.01 M ethylenediaminetetraacetate (EDTA), and determined by square-wave anodic stripping voltammetry (SWASV). Various factors influencing the determination of thallium(I) were thoroughly investigated. This modified electrode exhibits good resistance to interferences from surface-active compounds. The presence of EDTA effectively eliminated the interferences from metal ions, such as lead(II) and cadmium(II), which are generally considered as the major interferents in the determination of thallium at a mercury electrode. With 2-min preconcentration, linear calibration graphs were obtained over the range 0.05-100 ppb of thallium(I). An even lower detection limit, 0.01 ppb, were achieved with 5-min accumulation. The electrode is easy to prepare and can be readily renewed after each stripping experiment. Applicability of this procedure to various water samples is illustrated.     

Speciation of trace metals in natural waters: the influence of an adsorbed layer of natural organic matter (NOM) on voltammetric behaviour of copper

The influence of an adsorbed layer of the natural organic matter (NOM) on voltammetric behaviour of copper on a mercury drop electrode in natural water samples was studied. The adsorption of NOM strongly affects the differential pulse anodic stripping voltammogram (DPASV) of copper, leading to its distortion. Phase sensitive ac voltammetry confirmed that desorption of adsorbed NOM occurs in general at accumulation potentials more negative than −1.4 V. Accordingly, an application of negative potential (−1.6 V) for a very short time at the end of the accumulation time (1% of total accumulation time) to remove the adsorbed NOM was introduced in the measuring procedure. Using this protocol, a well-resolved peak without interferences was obtained. It was shown that stripping chronopotentiogram of copper (SCP) in the depletive mode is influenced by the adsorbed layer in the same manner as DPASV. The influence of the adsorbed NOM on pseudopolarographic measurements of copper and on determination of copper complexing capacity (CuCC) was demonstrated. A shift of the peak potential and the change of the half-peak width on the accumulation potential (for pseudopolarography) and on copper concentration in solution (for CuCC) were observed. By applying a desorption step these effects vanished, yielding different final results.     

The effects of CopperZinc and CopperCadmium intermetallic compounds in different systems used for anodic stripping voltammetry

The CuZn intermetallic compound resulting from simultaneous deposition of copper and zinc at a hanging mercury drop electrode (HMDE) and at preformed mercury film electrodes (MFE) has been studied. Goals were to determine what conditions can be used to avoid intermetallic compound formation and to reduce errors that result from the method of standard additions. For Cu²⁺ and Zn²⁺ concentrations in the ng ml⁻¹ range, the use of shortened preconcentration times in conjunction with a differential pulse stripping waveform and the HMDE show significant reduction in the extent of the interference. The CuCd interference was also characterized at performed MFE's and at MFE's deposited in situ from 5–300 μg ml⁻¹ mercury(II) solutions. No significant interference with the cadmium stripping were was observed with preformed MFE's, but peak depression was observed when the electrodes were deposited in situ. The degree of interference was found to decrease with both increased mercury(II) concentrationa and decreased copper(II) concentration. Errors in the standard addition method are minimal when the copper(II) concentration is not significantly altered.     

The determination of lead,copper and cadmium by anodic stripping voltammetry at a mercury thin-film electrode

The determination of lead, copper and cadmium by anodic stripping voltammetry at a wax-impregnated graphite electrode, pre-plated with mercury, has been investigated. Electrode preparation and cell design are discussed, and the effects of mercury loading and sample pH on electrode sensitivity are described. Detection limits and precision on aqueous samples are reported. Calibration graphs are linear for lead and cadmium, but non-linear for low concentrations of copper. The depression of peak current and shift of peak potential for copper in chloride media are described and an explanation is proposed. Precision and recovery of metal additions are reported for digested samples of whole blood.     

Intermetallic compounds and the determination of copper and zinc by anodic stripping voltammetry

The intermetallic CuZn compounds produced during the simultaneous deposition of copper and zinc at a preformed mercury film electrode were studied. Over a wide range of metal concentration ratios, the real concentrations of metals in the amalgam were calculated from the peak areas obtained by anodic stripping voltammetry. The results indicate the formation of CuZn (insoluble) and CuZn2 (soluble) compounds with K_so=5×10^?4 and β₂=100, respectively. The electrodeposition potential of ?0.85 V vs. SCE for the reduction of copper in presence of zinc is confirmed as correct.     

Determination of thallium in soils by differential pulse anodic stripping voltammetry by means of a mercury film electrode

Trace amounts of thallium can be determined in soils by differential pulse anodic stripping voltammetry with a mercury film electrode. The mercury film is plated ex situ on a glassy carbon surface. By using a supporting electrolyte of ascorbic acid and EDTA at pH 4.5 and the optimum electrolysis potential, interferences from lead and other metal ions can be eliminated. The method does not require any separation of thallium from the matrix. The results are in satisfactory agreement with those obtained by graphite furnace atomic absorption spectrometry.     

Catalytic hydrogen evolution in cathodic stripping voltammetry on a mercury electrode in the presence of cobalt(II) ion and phenylthiourea or thiourea.

The system Co(II)-phenylthiourea (PTU)-borax buffer was investigated by cathodic stripping voltammetry (CSV) at a hanging mercury drop electrode. The results of the voltammetric measurements showed that the presence of both PTU and Co(II) gives rise to a new irreversible peak at about -1.5 V. Based upon our previous results obtained in the study of other sulfur compounds and the sulfide ion itself, the peak was ascribed to the catalytic hydrogen evolution superimposed on the reduction of the coordinated Co(II) ion. The catalyst itself is a Co(II) complex with the sulfide ion produced by the decomposition of the analyte during the deposition step. The influence of PTU and cobalt concentration, accumulation conditions and stripping parameters was investigated and complementary data on thiourea are included. The results showed that the measurement of the catalytic hydrogen evolution peak current can be used as a basis for a simple, accurate and rapid method for the determination of PTU within the concentration range 10-100 nM. The catalytic method is relatively free of interferences and could be a suitable alternative for cases in which the stripping peak due to mercury ion reduction in the accumulated mercury compound is disturbed by some interference.     

Effect of mercury(II) on metal complex labilities determined by direct-current anodic stripping voltammetry on a thin mercury film electrode

The labilities of copper, lead and cadmium complexes with fulvic acid, nitrilotriacetic acid and an iron-humic acid colloid were studied on a preplated thin mercury film electrode and with in-situ plating of mercury on a glassy carbon electrode. In the presence of mercury(II) the apparent labilities based on direct-current anodic stripping voltammetric peak-area measurements increased for each of the cadmium and lead species and for the copper iron-humic acid colloid species. In contrast, for the copper complexes with nitrilotriacetic acid and fulvic acid the lability was not measurably altered by mercury(II); it is inferred that they do not undergo rapid metal exchange with mercury(II).     

The differential pulse anodic stripping voltammetry of copper and lead and their determination in EDTA extracts of soils with the mercury film glassy carbon electrode

The differential pulse anodic stripping voltammetry of copper and lead at the mercury film glassy carbon electrode is discussed. The mercury film prevents the occurrence of a monolayer stripping peak for copper. The influence of antimony and bismuth on the anodic stripping voltammetric behaviour of copper and lead is discussed. An interaction between copper and antimony distorts the copper stripping peak and gives rise to an intermediate peak. The method described is suitable for determining copper and lead simultaneously in EDTA extracts of soils.     

The use of Nafion-coated thin mercury film electrodes for the determination of the dissolved copper speciation in estuarine water

Differential pulse anodic stripping voltammetry (DPASV) using a Nafion-coated thin mercury film electrode (NCTMFE) was implemented to determine the dissolved copper speciation in saline estuarine waters containing high concentrations of dissolved organic matter (DOM). The study used model ligands and estuarine water from San Francisco Bay, California, USA to demonstrate that the NCTMFE is more effective at distinguishing between electrochemically inert and labile copper species when compared to the conventional thin mercury film electrode (TMFE). Copper titration results verify that the NCTMFE better deals with high concentrations of DOM by creating a size-exclusion barrier that prevents DOM from interacting with the mercury electrode when performing copper speciation measurements. Pseudovoltammograms were used to illustrate that copper complexes found in natural waters were more apt to be electrochemically inert at the NCTMFE relative to the TMFE when subjected to high negative overpotentials. Copper speciation results using the NCTMFE from samples collected in San Francisco Bay estimated that >99.9% of all copper was bound to strong copper-binding ligands. These L₁-class ligands exceeded the concentration of total dissolved copper in all samples tested and control the equilibrium of ambient [Cu²⁺] in the San Francisco Bay estuary.     

Chronopotentiometric Stripping Analysis Using Gold Electrodes,an Efficient Technique for Mercury Quantification in Natural Waters

This paper proposes a simple methodology for mercury quantification in natural water by stripping chronopotentiometry at constant current, using gold (film) electrodes constructed from recordable CDs in stationary cell. The proposed method allows the direct measurement of labile mercury in natural waters. To quantify total mercury, a robust and low cost UV irradiation system was developed for the degradation of organic constituents of water. The proposed system presents such advantages as excellent sensitivity, low cost, versatility, and smaller dimensions (portability for on‐field applications) when compared with other techniques (ICP, GFAAS, fluorimetry) traditionally utilized for mercury quantification. A large linear region of responses was observed, situated over the range 0.02–200 μg L^?1. Various experimental parameters were optimized and the system allowed quantifications in natural samples, with detection limit of 8 ng L^?1 and excellent reproducibility (RSD of 1.4% for 48 repetitive measurements using a 10 μg L^?1 mercury solution). Different metal ions were evaluated, including copper, as possible interferences on stripping mercury signals. Applications of the new method were demonstrated for the analysis of certified and groundwater samples spiked with a known amount of mercury and for the quantification of methylmercury in synthetic oceanic water, originally utilized for fishes contamination experiment.     

Voltammetric Determination of Mercury(II) at Poly(3‐hexylthiophene) Film Electrode. Effect of Halide Ions

The well‐known method for the determination of mercury(II), which is based on the anodic stripping voltammetry of mercury(II), has been adapted for applications at the thin film poly(3‐hexylthiophene) polymer electrode. Halide ions have been found to increase the sensitivity of the mercury response and shift it more positive potentials. This behavior is explained by formation of mercuric halide which can be easily deposited and stripped from the polymer electrode surface. The procedure was optimized for mercury determination. For 120 s accumulation time, detection limit of 5 ng mL^?1 mercury(II) has been observed. The relative standard deviation is 1.3% at 40 ng mL^?1 mercury(II). The performance of the polymer film studied in this work was evaluated in the presence of surfactants and some potential interfering metal ions such as cadmium, lead, copper and nickel.     

主成分回归-络合滴定法测定混合金属离子

提出了用络合滴定法测定混合金属离子.以汞膜电极为指示电极,银-氯化银电极为参比电极,以标准EDTA溶液滴定混合金属离子溶液.采集-系列指定电位点处滴定剂的体积,并以主成分回归法处理滴定数据.利用本文方法对铜、锌、铅、钻混合溶液进行了测定,结果满意.     

Determination of Cu, Pb, Cd, and Zn in river sediment extracts by sequential injection anodic stripping voltammetry with thin mercury film electrode

Determination of Cu, Pb, Cd and Zn was performed in sediment extracts obtained according to the three steps sequential extraction procedure proposed by the European Community Standards, Measurements and Testing Program. The metal content was determined by anodic stripping voltammetry with a thin mercury film electrode controlled by a sequential injection (SIA) system. The proposed method improved the reproducibility of conventional anodic stripping voltammetry, as well as the sample throughput, allowing analysis of 30 to 45 samples per hour. The influence of flow rate and sample volume was studied to achieve an adequate sensitivity for the leachate studied. No interferences due to adsorption of organic matter, colloids, or complexes with slow rate of dissociation were observed. The intermetallic formation of Cu-Zn was avoided by forming the mercury film in presence of Ga(III) ions in the SIA system, resulting in low consumption of reagent in comparison to flow injection or continuous flow systems. Results were in good agreement with those obtained by Induced Coupled Plasma - Atomic Emission Spectroscopy (ICP-AES).     

Electroanalysis of some nitro-compounds using bulk bismuth electrode

Nitro compounds were usually determined electrochemically using the mercury drop with DPP technique. An alternate way to toxic mercury is the increasing use of the bismuth electrode as thin film electrodeposited on glassy carbon or copper for example, or as bulk bismuth disc. In the present paper several nitrocompounds were investigated: mononitrophenols, dinitrophenol, nitrobenzoic acid, nitrobenzaldehyde and a well known pesticide, parathion, which has a nitro group in para position on a phenyl cycle. Bulk bismuth electrode was a disc (cross section of a rod of 5 mm diameter embedded in Teflon®) polished with silicon carbide disc (P2400) and sonicated to remove any abrasive particle. The supporting electrolyte was the acetic buffer (pH 4.7), which was found suitable for all these compounds. Using cathodic sweep differential pulse voltammetry, it was noticed that according to the position of the nitro group on the cycle, the peak potentials might range between ?300 to ?750 mV vs. SCE. Limits of detection (LOD) and limits of quantification (LOQ) were determined for each compound whose response for increasing concentration was linear in the ～3–50 µmol L^?1 whatever the considered molecule. Adsorptive differential pulse voltammetry was found very efficient to determine parathion, because this molecule adsorbs on bismuth at ?0.2 V vs. SCE. Bulk bismuth electrode was compared to the hanging mercury drop electrode and led to an identical behaviour.     

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.