Validation of bismuth film electrode for determination of cobalt and cadmium in soil extracts using ICP-MS

A study is presented on the use of the bismuth film electrode (BiFE) operated in the anodic stripping and the cathodic adsorptive stripping voltammetry (ASV, CAdSV) modes, for the determination of two trace heavy metals (Cd and Co, respectively), in soil extract samples. Two types of BiFE were examined in this study: the in situ prepared BiFE, which was employed in ASV determination of Cd, and the ex situ prepared BiFE, which was used in CAdSV of Co with dimethylglyoxime (DMG) as complexing agent. A series of unpretreated soil extracts with varying Cd and Co concentrations were analyzed, and the results obtained compared to those determined using inductively coupled plasma-mass spectrometry (ICP-MS). The results revealed the suitability of stripping analysis at the BiFE for determination of μg l⁻¹ levels of heavy metals in soil extracts. The promising results obtained here, coupled with the non-toxic nature of bismuth (in comparison to commonly used mercury electrodes employed in stripping analysis), offer great promise in centralized and decentralized analysis of trace heavy metals in complex environmental matrices.     

Ag(I)与Co(II)离子对阳极析氧过程的电催化作用

Influence of Ag(Ⅰ), Co(Ⅱ) and Ni(Ⅱ) ions on oxygen anodic evolution at Pt and Ti/Pt/PbO2 electrodes was investigated in surphuric acid solutions. The oxygen evolution reaction at Ti/Pt/PbO2 electrode in surphuric acid solutions is characterized by two linearφ~ lgi relationships. At low c.d. it is close to 2.303RT/(1+β)F, whereas at high c.d. it is close to 2.303RT/βF. In the presence of Ag(Ⅰ) or Ni(Ⅱ) ions in the electrolytic solution the Tafel slope of oxygen evolution tends to be low, 2.303RT/(1+β)F (withβ=0.5). However, the oxygen evolution reaction at Pt electrodes in H2SO4 or CoSO4﹢H2SO4 solutions is characterized by one linearφ~ lgi relationship. The Tafel slope is close to 2.303RT/βF. In the presence of Ag(Ⅰ) or Ni(Ⅱ) ions in the electrolytic solution the Tafel slope of oxygen evolution tends to be low, 2.303RT/(1+β)F. The oxygen anodic evolution reactions are catalyzed by Ag(Ⅰ), Co(Ⅱ) and Ni(Ⅱ) ions in the electrolytic solution. When Ag(Ⅰ) or Ni(Ⅱ) was mixed with Co(Ⅱ), a promising catalyst for oxygen anodic evolution with higher catalyst activity than either of them alone was found. A comparison of the PbO2 electrode and the Pt electrode has also been given.     

Bismuth film electrode for simultaneous adsorptive stripping analysis of trace cobalt and nickel using constant current chronopotentiometric and voltammetric protocol

Bismuth film electrode (BiFE) is presented as a promising alternative to mercury electrodes for the simultaneous determination of trace cobalt and nickel in non-deoxygenated solutions. The preplated BiFE was employed under adsorptive stripping constant current chronopotentiometric and adsorptive stripping voltammetric conditions in the presence of dimethylglyoxime complexing agent. BiFE exhibited well-defined and undistorted signals with favorable overall resolution for cobalt and nickel cations, with the signals for both metal cations being practically independent of each other. The stripping performance of BiFE is characterized by good reproducibility (RSD 1.4% for Co(II), and 4.3% for Ni(II)), low detection limits of 0.08 μg l⁻¹ for Co(II) and 0.26 μg l⁻¹ for Ni(II) employing a deposition time of 60 s, in addition to good linearity. The non-toxic character of bismuth imparts the possibility of tailoring disposable and one-shot electrochemical sensors for decentralized environmental, clinical and industrial monitoring of trace cobalt and nickel.     

Disposable mercury-free cell-on-a-chip devices with integrated microfabricated electrodes for the determination of trace nickel(II) by adsorptive stripping voltammetry

This work reports the fabrication of disposable three-electrode cells with integrated sputtered metal-film electrodes. The working electrode was a bismuth-film electrode (BiFE) while the reference and counter electrodes were made of Ag and Pt, respectively. The deposition of the metal layers was carried out by sputtering of the respective metals on a silicon substrate while the exact geometry of the electrodes was defined via a metal mask placed on the substrate during the deposition process. Initially, the electrodes were characterised by cyclic voltammetry. The utility of these devices was tested for the trace determination of Ni(II) by square wave adsorptive stripping voltammetry (SWAdSV) after complexation with dimethylglyoxime (DMG). The experimental variables (the presence of oxygen, the DMG concentration, the preconcentration potential, the accumulation time and the SW parameters), as well as potential interferences, were investigated. Using the selected conditions, the 3sigma limit of detection was 100 ng L(-1) for Ni(II) (for 90 s of preconcentration) and the relative standard deviation for Ni(II) was 2.3% at the 10 microg L(-1) level (n=8). Finally, the method was applied to the determination of Ni(II) in a certified river water sample.     

Selective determination of Ni(II) and Co(II) by flow injection analysis and adsorptive cathodic stripping voltammetry on a wall jet mercury film electrode

Ni(II) and Co(II) have been determined simultaneously by means of adsorptive cathodic stripping voltammetry (AdCSV) in a computerised flow injection system. The working electrode was a glassy carbon disk that was fitted in a wall-jet flow cell. The electrode was initially electrochemically coated with a mercury film at -1.0 V by injecting a Hg(II) solution in the flow stream. Then, the sample, containing Ni(II) and Co(II), was mixed on-line with a solution containing dimethylgyoxime (DMG) at pH 9 in order to selectively complex the metal ions and was injected in the flow system. After a number of successive injections during which accumulation took place under controlled potentiostatic conditions, the surface-bound complexes were reduced in ammonia buffer at pH 9 by a cathodic scan of the potential of the working electrode in the square wave mode and the current-potential response was recorded. Finally, the electrode surface was regenerated by a potentiostatic polarisation at -1.4 V in the same buffer. The apparatus could be easily converted for continuous flow accumulation in order to increase the sensitivity; in this mode of operation, instead of performing discrete injections, the sample was continuously pumped through the cell. Various parameters associated with the preconcentration, stripping and regeneration steps were optimised for the determination of Ni(II) and Co(II). The selectivity of the method was demonstrated for the analysis of high purity iron; the accuracy for the determination of Ni(II) and Co(II) was 11 and 3%, respectively while the coefficient of variation was 10 and 8%, respectively.     

Determination of trace cobalt(II) by adsorptive stripping voltammetry on disposable microfabricated electrochemical cells with integrated planar metal-film electrodes

This work reports the determination of trace Co(II) by adsorptive stripping voltammetry on disposable three-electrode cells with on-chip metal-film electrodes. The heart of the sensors was a bismuth-film electrode (BiFE) with Ag and Pt planar strips serving as the reference and counter electrodes, respectively. Metals were deposited on a silicon chip by sputtering while the areas of the electrodes were patterned via a metal mask. Co(II) was determined by square wave adsorptive stripping voltammetry (SWAdSV) after complexation with dimethylglyoxime (DMG). The experimental variables (the DMG concentration, the preconcentration potential, the accumulation time and the SW parameters), as well as potential interferences, were investigated. Using the selected conditions, the 3σ limit of detection was 0.09 μg l⁻¹ of Co(II) (for 90 s of preconcentration) and the relative standard deviation for Co(II) was 3.8% at the 2 μg l⁻¹ level (n = 8). The method was applied to the determination of Co(II) in a certified river water sample. These mercury-free electrochemical devices present increased scope for field analysis and μ-TAS applications.     

Sequential injection monosegmented flow voltammetric determination of cadmium and lead using a bismuth film working electrode

A cost-effective sequential injection monosegmented flow analysis (SI-MSFA) with anodic stripping voltammetric (ASV) detection has been developed for determination of Cd(II) and Pb(II). The bismuth film working electrode (BiFE) was employed for accumulative preconcentration of the metals by applying a fixed potential of −1.10 V versus Ag/AgCl electrode for 90 s. The SI-MSFA provides a convenient means for preparation of a homogeneous solution zone containing sample in an acetate buffer electrolyte solution and Bi(III) solution for in situ plating of BiFE, ready for ASV measurement at a flow through thin layer electrochemical cell. Under the optimum conditions, linear calibration graphs in range of 10-100 μg L⁻¹ of both Cd(II) and Pb(II) were obtained with detection limits of 1.4 and 6.9 μg L⁻¹ of Cd(II) and Pb(II), respectively. Relative standard deviations were 2.7 and 3.1%, for 11 replicate analyses of 25 μg L⁻¹ Cd(II) and 25 μg L⁻¹ Pb(II), respectively. A sample throughput of 12 h⁻¹ was achieved with low consumption of reagent and sample solutions. The system was successfully applied for analysis of water samples collected from a draining pond of zinc mining, validating by inductively coupled plasma-optical emission spectroscopy (ICP-OES) method.     

Methanol electrooxidation on novel modified carbon paste electrodes with supported poly(isonicotinic acid) (sodium dodecyl sulfate)/Ni-Co electrocatalysts

Poly(isonicotinic acid) (PINA) was formed by successive cyclic voltammetry in monomer solution in the presence of sodium dodecyl sulfate (SDS) on the surface of a carbon paste electrode (CPE). Ni(II) and Co(II) ions were incorporated into the electrode by immersion of the polymer-modified electrodes in Ni(II) and Co(II) ion solutions in different proportions. After the preparation of modified electrodes, their electrochemical behavior was studied by cyclic voltammetric experiments. Electrocatalytic oxidation of methanol at the surface of the modified electrodes was studied in 1?M NaOH solution. These modified electrodes exhibit high electrocatalytic activity and stability in alkaline solution, showing oxidation peaks at low potentials with high current densities. The electrooxidation of methanol was found to be more efficient on CPE/PINA(SDS)/Ni₈₀Co₂₀ than on CPE/PINA(SDS)/Ni and CPE/PINA(SDS)/Ni₅₀Co₅₀. The effects of various parameters such as scan rates and methanol concentration on the electrooxidation of methanol are also investigated.     

An introduction to bismuth film electrode for use in cathodic electrochemical detection

A new electrode surface design, the bismuth film electrode (BiFE), is presented as a promising alternative to mercury and other solid electrodes for direct cathodic electrochemical detection of organic compounds. The preparation of the BiFE, involving an ex situ electroplating of metallic bismuth onto a glassy carbon (GC) substrate electrode, was optimised. The useful negative potential windows of the BiFE in the pH range 1 (−0.2 to −0.8 V vs Ag/AgCl) to 10 (−0.2 to −1.5 V) were determined. The reproducibility of measuring 2-nitrophenol as a model compound (relative standard deviation, r.s.d., n=10) was found to be 0.5% at the same BiFE, and 1.0% at successive newly prepared BiFEs. No polishing or any other pre-treatment of the substrate GC surface was required prior to re-plating of a new Bi film. The BiFE showed similar or even favourable voltammetric behaviour when compared to mercury and bare GC electrodes, and was successfully tested for amperometric detection under hydrodynamic conditions. The results revealed that BiFE is an attractive new non-mercury metallic electrode particularly suitable for cathodic electrochemical detection in flow analytical systems.     

Automated portable analyzer for lead(II) based on sequential flow injection and nanostructured electrochemical sensors

A fully automated portable analyzer for toxic metal ion detection based on a combination of a nanostructured electrochemical sensor and a sequential flow injection system has been developed in this work. The sensor was fabricated from a carbon paste electrode modified with acetamide phosphonic acid self-assembled monolayer on mesoporous silica (Ac-Phos SAMMS) which was embedded in a very small wall-jet (flow-onto) electrochemical cell. The electrode is solid-state and mercury-free. Samples and reagents were injected into the system and flowed through the electrochemical cell by a user programmable sequential flow technique which required minimal volume of samples and reagents and allowed the automation of the analyzer operation. The portable analyzer was evaluated for lead (Pb) detection due to the excellent binding affinity between Pb and the functional groups of Ac-Phos SAMMS as well as the great concern for Pb toxicity. Linear calibration curve was obtained in a low concentration range (1-25 ppb of Pb(II)). The reproducibility was excellent; the percent relative standard deviation was 2.5 for seven consecutive measurements of 10 ppb of Pb(II) solution. Excess concentrations of Ca, Ni, Co, Zn, and Mn ions in the solutions did not interfere with detection of Pb, due to the specificity and the large number of the functional groups on the electrode surface. The electrode was reliable for at least 90 measurements over 5 days. This work is an important milestone in the development of the next-generation metal ion analyzers that are portable, fully automated, and remotely controllable.     

Voltammetric Determination of Trace Heavy Metals by Sequential-injection Analysis at Plastic Fluidic Chips with Integrated Carbon Fiber-based Electrodes

This work describes a sequential injection analysis (SIA) method for on-line strippping voltammetric determination of Pb(II), Cd(II) and Zn(II) using an injection-moulded electrochemical fluidic chip consisting of 3 conductive carbon fiber-loaded polymer electrodes embedded in a plastic fluidic holder. The sample containing the target metals and a solution containing Bi(III) were aspirated in the holding coil of the SIA manifold. Then, the flow was reversed and the two solutions were directed to the fluidic cell through a mixing coil which induced mixing of the two zones. Upon reaching the cell, simultaneous reduction of the target metals and Bi(III) occurred resulting in the formation of a metal-Bi alloy on the working electrode. Finally, the accumulated metals were stripped off the bismuth-film electrode via a positive potential scan and the oxidation current was recorded. The experimental variables (concentration of the bismuth plating solution, deposition potential, sample volume, stripping mode) were investigated and the potential interferences were assessed. The limits of quantification were 2.8 μg L⁻¹ for Pb(II), 3.6 μg L⁻¹ for Cd(II) and 4.2 μg L⁻¹ for Zn(II) and the the within-chip and between-chip % relative standard deviations were ≤6.3 % and ≤14 %, respectively. Finally, the sensor was applied to the determination of trace metals in a fish food sample.     

Continuous-flow performance of carbon electrodes modified with immobilized Fe(II)/Fe(III) centers Amperometric response to N(2)O, NO and NO(2)

The amperometric performance of two types of chemically modified carbon electrodes developed for the determination of oxides of nitrogen in continuous-flow systems is presented. The modification consists in immobilization of reversible Fe(II)/Fe(III) centers. The first type of electrode is a simple modification made by direct mixing of carbon paste with tris-4,7-diphenyl-1,10-phenanthroline-iron(II) perchlorate; the other is a glassy-carbon surface modified by oxidative electropolymerization of tris-[5-amino-1,10-phenanthroline]iron(II) perchlorate. Detection is accomplished by transporting an injected sample plug to the sensing surface with the aid of gravitational flow of an aqueous solution of supporting electrolyte. The polymer-coated electrochemical detector compares favourably with the chemically modified carbon paste. It offers excellent resistance to poisoning and a competitive limit of detection [about 2 ppb (2 parts in 10(9)) v/v], at + 1.0 V vs. Ag/AgCl, and good selectivity for NO(2) when used in a thin-layer cell. Incorporation of the cell in a continuous-flow system allows injection of about 120 samples per hour. The typical concentration range amenable to determination is 2-25 ppb v/v but depends on the thickness of the polymeric film. Nitrogen monoxide can also be detected but only in undiluted, pure form. Dinitrogen oxide gives no amperometric signal at any of the modified surfaces.     

A Study on Operational Parameters for Advanced Use of Bismuth Film Electrode in Anodic Stripping Voltammetry

A study is presented on the characterization, evaluation and optimization of several key operational parameters for a reliable and effective use of a bismuth film electrode (BiFE) as an advanced replacement of the mercury film electrode in anodic stripping voltammetric measurements of trace heavy metals. Applying in situ preparation of the BiFE and employing lead(II) and cadmium(II) as model analyte ions, key parameters including bismuth precursor salt and substrate surface (platinum, gold, glassy carbon, carbon paste, carbon fiber) for bismuth plating, concentration as well as cationic and anionic composition of the measurement solution, solution pH and temperature, potential interferents, and stripping modes were carefully examined for their effects in the preconcentration and stripping steps. Parameters such as substrate surface (except platinum), precursor salt, solution matrix and temperature showed no or little impact on the BiFE performance in stripping analysis. On the other hand, the BiFE performance was found to be dependent on the solution pH (with maximum efficiency in the range of 4 to 5), on the stripping mode (with square‐wave voltammetry as the best choice) and to a certain degree on the presence of surface active substances. The results revealed that the non‐toxic solid‐state BiFE is applicable under a wide variety of conditions which proves it highly suitable for practical work in environmental trace heavy metal analysis.     

Determination of trace Pb(Ⅱ), Cd(Ⅱ) and Zn(Ⅱ) using differential pulse stripping voltammetry without Hg modification

In this work,we reported a simultaneous determination approach for Pb(II),Cd(II)and Zn(II)atμg L 1concentration levels using differential pulse stripping voltammetry on a bismuth film electrode(BiFE).The BiFE could be prepared in situ when the sample solution contained a suitable amount of Bi(NO)3,and its analytical performance was evaluated for the simultaneous determination of Pb(II),Cd(II)and Zn(II)in solutions.The determination limits were found to be 0.19μg L 1for Zn(II),and0.28μg L 1for Pb(II)and Cd(II),with a preconcentration time of 300 s.The BiFE approach was successfully applied to determine Pb(II),Cd(II)and Zn(II)in tea leaf and infusion samples,and the results were in agreement with those obtained using an atomic absorption spectrometry approach.Without Hg usage,the in situ preparation for BiFE supplied a green and acceptability sensitive method for the determination of the heavy metal ions.     

On-line stripping voltammetry of trace metals at a flow-through bismuth-film electrode by means of a hybrid flow-injection/sequential-injection system

In this work, we describe an automated stripping analyzer operating on a hybrid flow-injection/sequential-injection (FIA/SIA) mode and utilizing a bismuth-film electrode (BiFE) as a flow-through sensor for on-line stripping voltammetry of trace metals. The instrument combines the advantages of FIA and SIA and is characterised by simplicity, low-cost, rapidity, versatility and low consumption of solutions. The proposed analytical flow methodology was applied to the determination of Cd(II) and Pb(II) by anodic stripping voltammetry (ASV) and of Ni(II) and Co(II) by adsorptive stripping voltammetry (AdSV). The steps of the rather complex experimental sequence (i.e. the bismuth-film formation, the analyte accumulation, the voltammetric stripping and the electrode cleaning/regeneration) were conducted on-line and the critical parameters related to the respective analytical procedures were investigated. In ASV, for a accumulation time of 180 s the limits of detection for Cd(II) and Pb(II) were 2 and 1 μg l⁻¹, respectively (S/N = 3) and the relative standard deviations were 5.3% and 4.7%, respectively (n = 8). In AdSV, for a total sample volume of 1000 μl, the limits of detection for Ni(II) and Co(II) were 1 μg l⁻¹ (S/N = 3) and the relative standard deviations were 5.5% and 6.2%, respectively (n = 8). The measurement frequency ranged between 15 and 20 stripping cycles h⁻¹. The results indicate that the BiFE is well suited as a flow-through detector for on-line stripping analysis and, by virtue of its low toxicity, can serve as a viable alternative to mercury-based flow-through electrodes.     

Simultaneous Determination of Cadmium,Lead, Copper,and Thallium in Highly Saline Samples by Anodic Stripping Voltammetry (ASV) Using Mercury‐Film and Bismuth‐Film Electrodes

This paper describes a comparative study of the simultaneous determination of Cd(II), Pb(II), Tl(I), and Cu(II) in highly saline samples (seawater, hydrothermal fluids, and dialysis concentrates) by ASV using the mercury‐film electrode (MFE) and the bismuth‐film electrode (BiFE) as working electrodes. The features of MFE and BiFE as working electrodes for the single‐run ASV determinations are shown and their performances are compared with that of HMDE under similar conditions. It was observed that the stripping peak of Tl(I) was well separated from Cd(II) and Pb(II) peaks in all the studied saline samples when MFE was used. Because of the severe overlapping of Bi(III) and Cu(II) stripping peaks in the ASV using BiFE, as well as the overlapping of Pb(II) and Tl(I) stripping peaks in the ASV using HMDE, the simultaneous determination of these metals was not possible in highly saline medium using these both working electrodes. The detection limits calculated for the metals using MFE and BiFE (deposition time of 60 s) were between 0.043 and 0.070 μg L^?1 for Cd(II), between 0.060 and 0.10 μg L^?1 for Pb(II) and between 0.70 and 8.12 μg L^?1 for Tl(I) in the saline samples studied. The detection limits calculated for Cu(II) using the MFE were 0.15 and 0.50 μg L^?1 in seawater/hydrothermal fluid and dialysis concentrate samples, respectively. The methods were applied to the simultaneous determination of Cd(II), Pb(II), Tl(I), and Cu(II) in samples of seawater, hydrothermal fluids and dialysis concentrates.     

Voltammetric determination of lead at chemically modified electrodes based on crown ethers.

The feasibility of fabricating lead-sensitive chemically modified electrodes (CMEs) for trace analysis in aqueous and 40% (v/v) ethanol-water media was investigated. Carbon paste electrodes modified with crown ethers were constructed by mixing the crown ethers into a graphite powder-paraffin oil matrix. The thus-formed electrodes were able to bind Pb(II) ions chemically, and gave better voltammetric responses than unmodified ones. The crown ethers studied and compared were 18-crown-6 and dibenzo-18-crown-6. With a 5% 18-crown-6 CME, Pb(II) could be quantified at sub-ppm levels by differential pulse voltammetry with a detection limit of 0.02 ppm. It was possible to selectively pick up Pb(II) from a solution of several other ions at an open circuit through complexation. A simultaneous analysis of Cu(II) and Pb(II) was also attempted. By differential pulse anodic stripping voltammetry Pb(II) could be quantified over the range of 1 to 100 ppb. Interference from metal ions like Ni(II), Co(II), Mn(II), Zn(II), Cd(II), Ag(I), Fe(III), Ca(II) and Mg(II) was also studied. The method was successfully applied to artificial as well as commercial samples of alcoholic beverages.     

Disposable Screen-Printed Electrodes (Spe) Mercury-Free for Lead Detection

ABSTRACT

Strategies to modify screen-printed electrodes (SPE) for lead determination are reported. Dithizone was mixed with graphite ink to obtain a modified screen-printed strip to detect ppb levels of lead(II) (detection limit 12 μg/l) using square wave anodic stripping voltammetry (SWASV). In addition, screen-printed electrodes were also modified by casting a few μl of a Nafion® solution onto the working electrode surface. In this case, ppb levels of lead were detected (detection limit 15 μg/1), using potentiometric stripping analysis (PSA). The addition of an ionophore to Nafion® polymer was also investigated, but this did not yield a significant improvement.     

Bismuth film electrodes for the study of metal thiolate complexation: An alternative to mercury electrodes

A comparative study of the usual static mercury drop electrode (SMDE) and the bismuth film electrode (BiFE) as applied to the analysis of metal complexation by thiol-rich peptides is done. Preliminary experiments on BiFE by differential pulse voltammetry showed that Cd(II) and Pb(II)-ions behave in a similar way as using stripping voltammetry and stripping chronopotentiometry with regard to some splitting effects of the signals. Additionally, on BiFE glutathione (GSH) and some phytochelatins (PC_n) produce quite irregular signals related to the anodic oxidation of bismuth, which restricted the studies to a narrower concentration range than on SMDE. In the presence of both metal ion and peptide the same characteristic signals were observed on BiFE and SMDE, but better resolution was achieved in the first one, allowing a qualitative analysis of the complexation process for the Pb-GSH system which was not possible on SMDE. This suggests that BiFE may be a complementary tool to Hg electrodes, if not a valuable alternative, in the study of metal complexation.     

Amperometric Determination of Cr(III) and Cr(VI) by Flow Injection Analysis

Speciation of Cr(III) and Cr(VI) can be attained by flow injection analysis with amperometric detection. Cr(VI) is reduced in an acidic medium to Cr(III) with a glassy carbon electrode at —0.1 V vs. Ag/AgCl and the current is recorded. Cr(III) is oxidised on-line to Cr(VI) with alkaline hydrogen peroxide solution. From the difference of the total chromium and Cr(VI), the amount of Cr(III) was obtained. A linear calibration curve for Cr(VI) was obtained for the concentration ranges 0.01-5.0ppm of Cr(VI) and we have calculated the limit of determination to be about 0.5ppb. We have studied the degree of reproducibility obtained using the solid electrodes under various conditions. The influence of flow rate, coil length, interfenences and the extent of reaction were studied.