Anodic stripping voltammetric measurement of trace heavy metals at antimony film carbon paste electrode

The antimony film carbon paste electrode (SbF-CPE) was prepared in situ on the carbon paste substrate electrode as a “mercury-free” electrochemical sensor. Its aptitude for measuring some selected trace heavy metals has been demonstrated in combination with square-wave anodic stripping voltammetry in non-deaerated model solutions of 0.01 M hydrochloric acid with pH 2. Some important operational parameters, such as deposition potential, deposition time, and concentration of antimony ions were optimized, and the electroanalytical performance of the SbF-CPE was critically compared with both bismuth film carbon paste electrode (BiF-CPE) and mercury film carbon paste electrode (MF-CPE) using Cd(II) and Pb(II) as test metal ions. In comparison with BiF-CPE and MF-CPE, the SbF-CPE exhibited superior electroanalytical performance in more acidic medium (pH 2) associated with favorably low hydrogen evolution, improved stripping response for Cd(II), and moreover, stripping signals corresponding to Cd(II) and Pb(II) at the SbF-CPE were slightly narrower than those observed at bismuth and mercury counterparts. In addition, the comparison with antimony film electrode prepared at the glassy carbon substrate electrode displayed higher stripping current response recorded at the SbF-CPE. The newly developed sensor revealed highly linear behavior in the examined concentration range from 5 to 50 μg L⁻¹, with limits of detection (3σ) of 0.8 μg L⁻¹ for Cd(II), and 0.2 μg L⁻¹ for Pb(II) in connection with 120 s deposition step, offering good reproducibility of ±3.8% for Cd(II), and ±1.2% for Pb(II) (30 μg L⁻¹, n = 10). Preliminary experiments disclosed that SbF-CPE and MF-CPE exhibit comparable performance for measuring trace concentration levels of Zn(II) in acidic medium with pH 2, whereas its detection with BiF-CPE was practically impossible. Finally, the practical applicability of SbF-CPE was demonstrated via measuring Cd(II) and Pb(II) in a real water sample.     

Effect of Bi(III) concentration on the stripping voltammetric response of in situ bismuth-coated carbon paste and gold electrodes

The effect of Bi(III) concentration (over the wide concentration range of 10⁻⁷ to 10⁻⁴ M) on the determination of Pb and Cd metal ions (in the 10⁻⁸ to 10⁻⁵ M range), by means of anodic stripping voltammetry (ASV) at in situ bismuth-coated carbon paste (CPE) and gold electrodes, has been studied. It is shown that in square wave anodic stripping voltammetry (SWASV) experiments the sensitivity of the technique generally depends on the Bi(III)-to-metal ion concentration ratio. It was found that, unlike the usually recommended at least 10-fold Hg(II) excess in anodic stripping experiments at in situ prepared mercury film electrodes, Bi(III)-to-metal ion ratios less than 10 are either optimal or equally effective at CPE and Au electrode substrates. Detection limits down to 0.1 μg L⁻¹ for Pb(II) and 0.15 μg L⁻¹ for Cd(II) were estimated at CPEs under conditions of small or moderate Bi(III) excess. Depending on Bi(III) concentration and deposition time, multiple stripping peaks attributed to Bi were recorded (especially in the case of Au substrates), indicating various forms of Bi deposits.     

Current efficiency studies of the zinc electrowinning process on aluminum rotating cylinder electrode (RCE) in sulfuric acid medium: Influence of different additives

This work studies the effect of three additives, sodium lauryl sulfate (SLS), cetyltrimethylammonium bromide (CTABr) and arabic gum (AG) on zinc electrowinning on aluminum in a solution of 85 g L⁻¹ Zn(II) (1.3 M) in 108 g L⁻¹ H₂SO₄ (1.1 M). The influence of these three additives is analyzed during the different stages of the reduction process using chronopotentiometric techniques on an aluminum rotating disk electrode (RDE). Potential ranges (−1.05 < E < −0.85 V versus SHE) and current density (−51 < i < −0.2 mA cm⁻²) within which zinc electrodeposition takes place in the presence of the three different additives were established. These parameters were used to determine current efficiencies (Φ), evaluated by electrolysis on an aluminum rotating cylinder electrode (RCE); the zinc deposition efficiency in the presence of SLS, CTABr and AG, was 95%, 96% and 99%, respectively, were all greater than the efficiency obtained without any additive (WA), Φ = 84%. The homogeneity of the deposits at the end of electrolyses implied that the (RCE) promotes uniform current density on the electrode surface and, hence, can be considered a model cell to evaluate current efficiencies.     

Study and determination of the herbicide cyclosulfamuron by square wave stripping voltammetry

The voltammeric behavior of the herbicide cyclosulfamuron has been studied by square wave stripping voltammetry (SWSV). Cyclosulfamuron was reduced on a static mercury drop electrode (SMDE) and gave a well-defined peak in the pH range of 3.0-7.0. The peak potential (E_p) shifts to a more negative potential with increasing pH. The ratio ΔE_p/ΔpH over the pH range studied was 59.5 mV/pH. A systematic study of the various experimental parameters that affect the stripping response was studied by SWV. The square wave parameters used were a frequency of 150 Hz, an amplitude of −60 mV and a staircase step of 6.0 mV. The quantifications were performed by the standard addition method, from the SW voltammetric peak obtained at −1348 mV. Calibration curves were linear in the range of 10-350 μg L⁻¹ with a detection limit of 3.5 μg L⁻¹ under the conditions used (pH 6.0 buffer solution, E_acc = −400 mV vs. Ag/AgCl, t_acc = 75 s). The validity of the developed methodology was assessed by recovery experiments at the 25-100 μg L⁻¹ level. The mean results for 3 determinations were 49.7 ± 3.3 μg L⁻¹, which is very close to the amount of cyclosulfamuron added to soil (50 μg L⁻¹), with a recovery of 99.4%. The sufficiently good recoveries and low relative standard deviation (RSD) data reflects the high accuracy and precision of the proposed SW voltammetric method. The possible influences of various inorganic species and other pesticides were also investigated.     

Antimony powder-modified carbon paste electrodes for electrochemical stripping determination of trace heavy metals

A new type of the antimony electrode based on a carbon paste bulk-modified with antimony powder (Sb-CPE) is presented for the determination of cadmium(II) and lead(II) ions at the microgram-per-liter concentration level, when using square-wave anodic stripping voltammetric or stripping chronopotentiometric protocol. The Sb-CPE was prepared by mixing fine antimony powder, carbon powder, and silicon oil, thus combining typical features of the carbon paste material with specific electrochemical properties of antimony. Key-operational parameters, including the amount of antimony powder in the carbon paste mixture, effect of the deposition potential and deposition time, were optimized and electroanalytical performance of the Sb-CPE in nondeaerated solution of 0.01 M hydrochloric acid (pH 2) was compared with related bismuth powder-modified carbon paste electrode (Bi-CPE) and with in situ prepared antimony film carbon paste electrode (SbF-CPE). The electrode of interest exhibited well-developed signals and highly linear calibration plots for both metal ions tested. In addition, favorable limits of detection were achieved; namely: 1.4 μg L⁻¹ for Cd(II) and 0.9 μg L⁻¹ for Pb(II). The applicability of the new electrode was demonstrated on the analysis of tap water (spiked sample). Besides voltammetric measurements, the Sb-CPE was preliminary tested also under chronopotentiometric stripping mode in deoxygenated solutions, revealing also an excellent electroanalytical performance.     

Development of screen-printed carbon electrodes modified with functionalized mesoporous silica nanoparticles: Application to voltammetric stripping determination of Pb(II) in non-pretreated natural waters

A screen-printed carbon electrode modified with functionalized mesoporous silica nanoparticles (MTTZ-MSU-2) was developed and evaluated for reliable quantification of trace Pb(II) ions by anodic stripping square wave voltammetry in non-pretreated natural waters. The optimal operating conditions were 5 min preconcentration time and 120 s electrolysis time in HCl 0.2 M. The electrode displayed excellent linear behavior in the concentration range examined (1-30 μg L⁻¹) with a limit of detection of 0.1 μg L⁻¹. The screen-printed carbon modified electrode has long service time and good single and inter-electrode reproducibility. Applicability to spiked drinking water, river water and groundwater was demonstrated without any sample pre-treatment (recoveries between 97% and 106%, RSD 4-7%). On the basis of the present data, mercury-free screen-printed electrodes modified with functionalized mesoporous silicas have the potential to become the next-generation analyzers for decentralized heavy metal monitoring in environmental samples.     

Application of bismuth-film electrode for cathodic electroanalytical determination of sulfadiazine

A bismuth-film electrode for use in cathodic electrochemical detection was employed in order to quantify sulfadiazine in pharmaceutical formulations. The bismuth film was deposited ex situ onto a glassy carbon substrate. Analysis of two sulfa drugs was carried out by differential-pulse voltammetry in 0.05 mol L⁻¹ Britton-Robinson pH 4.5 solution. Sulfadiazine reduction was observed at −0.74 V vs. Ag/AgCl in one well-resolved irreversible reduction peak. The analytical curve with two slopes was obtained in the concentration range of 3.2-97.0 μmol L⁻¹. The detection limit was 2.1 μmol L⁻¹ for concentrations of 3.2-20.0 μmol L⁻¹ (r = 0.9949) and 12.2 μmol L⁻¹ for concentrations between 20.0 and 97.0 μmol L⁻¹ (r = 0.9951). Recovery studies carried out with both sulfadiazine samples gave values from 93.6 to 109.3%. The accuracy of the results supplied by the bismuth-film electrode was compared to those obtained by the standard amperometric titration method. The relative error between them was lower than 2.0%.     

Sensitive determination of Cd and Pb by differential pulse stripping voltammetry with in situ bismuth-modified zeolite doped carbon paste electrodes

Here we investigated the analytical performances of the bismuth-modified zeolite doped carbon paste electrode (BiF-ZDCPE) for trace Cd and Pb analysis. The characteristics of bismuth-modified electrodes were improved greatly via addition of synthetic zeolite into carbon paste. To obtain high reproducibility and sensitivity, optimum experimental conditions for bismuth deposition were studied. Voltammetric responses of the BiF-ZDCPEs prepared with different ratios of zeolite, carbon powder, and silicone, were examined under same conditions. The in situ plated (zeolite/graphite powder/silicone, 10/190/80 w/w) BiF-ZDCPEs exhibited the most sensitive response to Cd and Pb in 0.10 M acetate buffer (pH 4.5). The detection limits of the modified electrode were 0.08 μg L⁻¹ for Cd(II) and 0.10 μg L⁻¹ for Pb(II) based on three times the standard deviation of the baseline with a preconcentration time of 120 s under optimal conditions, respectively. The modified electrode showed well linear response to both Cd(II) and Pb(II) over the concentration range from 1.0 to 20.0 μg L⁻¹. The BiF-ZDCPEs were successfully applied to the determination of Cd(II) and Pb(II) in real samples, and the results were in agreement with those of atomic absorption spectroscopy (AAS).     

The ultrasonic electropolymerization of an 5-[o-(4-bromine amyloxy)phenyl]-10,15,20-triphenylporphrin (o-BrPETPP) film electrode and its electrocatalytic properties to dopamine oxidation in aqueous solution

5-[o-(4-Bromine amyloxy)phenyl]-10,15,20-triphenylporphrin (o-BrPETPP) was electropolymerized on a glassy carbon electrode (GCE), and the electrocatalytic properties of the prepared film electrode response to dopamine (DA) oxidation were investigated. A stable o-BrPETPP film was formed on the GCE under ultrasonic irradiation through a potentiodynamic process in 0.1 M H₂SO₄ between −1.1 V and 2.2 V versus a saturated calomel electrode (SCE) at a scan rate of 0.1 V s⁻¹. The film electrode showed high selectivity for DA in the presence of ascorbic acid (AA) and uric acid (UA), and a 6-fold greater sensitivity to DA than that of the bare GCE. In the 0.05 mol L⁻¹ phosphate buffer (pH 6.0), there was a linear relationship between the oxidation current and the concentration of DA solution in the range of 5 × 10⁻⁷ mol L⁻¹ to 3 × 10⁻⁵ mol L⁻¹. The electrode had a detection limit of 6.0 × 10⁻⁸ mol L⁻¹(S/N = 3) when the differential pulse voltammetric (DPV) method was used. In addition, the charge transfer rate constant k = 0.0703 cm s⁻¹, the transfer coefficient α = 0.709, the electron number involved in the rate determining step n_α = 0.952, and the diffusion coefficient D_o = 3.54  10⁻⁵ cm² s⁻¹ were determined. The o-BrPETPP film electrode provides high stability, sensitivity, and selectivity for DA oxidation.     

A novel graphite-polyurethane composite electrode modified with thiol-organofunctionalized silica for the determination of copper ions in ethanol fuel

A graphite-polyurethane composite modified with 2-benzothiazolethiol organofunctionalized silica was evaluated as an alternative electrode in the determination of Cu²⁺ ions in ethanol fuel samples, on the basis of a differential pulse anodic stripping voltammetry procedure. This metal can be quantified by mixing ethanol fuel with 0.10 mol L⁻¹ KNO₃ aqueous solution and subsequent voltammetric measurement after the accumulation step. A maximum limit of 70% (v/v) ethanol in potassium nitrate aqueous solution was obtained for voltammetric measurements without loss of sensitivity for metal species. Factors affecting the pre-concentration and stripping steps were investigated and optimum conditions were employed to develop the analytical procedure. Using 20 min of accumulation time, the linear range of 0.1-1.2 μmol L⁻¹ was obtained with the limit of detection of 3.9 × 10⁻⁸ mol L⁻¹. The developed electrode was successfully applied to determine Cu²⁺ in commercial ethanol fuel samples. The proposed method was compared with a traditional analytical technique, the flame atomic absorption spectrometry, and no significant differences between the results obtained by both methods were observed according to statistical evaluation.     

Electrochemical determination of bromide at a multiwall carbon nanotubes-chitosan modified electrode

A multiwall carbon nanotubes (MWNTs)-chitosan modified glassy carbon electrode (GCE) exhibits attractive ability for highly sensitive cathodic stripping voltammetric measurements of bromide (Br⁻). In pH 1.8 H₂SO₄ solution, a substantial increase in the stripping peak current of Br⁻ (compared to bare GCE and chitosan modified GCE) is observed using MWNTs-chitosan modified electrode. Operational parameters were optimized and the electrochemical behaviors of Br⁻ were studied by different electrochemical methods. The kinetics parameters were measured, the number of electron transfer (n) was 1 and the transfer coefficient (α) is 0.17. A wide linear calibration range (3.6 × 10⁻⁷-1.4 × 10⁻⁵ g mL⁻¹) was achieved, with a detection limit of 9.6 × 10⁻⁸ g mL⁻¹. The mechanism of electrode reaction was fully discussed.     

Electrocatalytic oxidation of ascorbic acid by [Fe(CN)6] redox couple electrostatically trapped in cationic N,N-dimethylaniline polymer film electropolymerized on diamond electrode

Multinegatively charged metal complex, hexacyanoferrate ([Fe(CN)₆]⁴⁻), was electrostatically trapped in the cationic polymer film of N,N-dimethylaniline (PDMA) which was electrochemically deposited on the boron-doped diamond (BDD) electrode by controlled-potential electro-oxidation of the monomer. This ferrocyanide-trapped PDMA film was used to catalyze the oxidation of ascorbic acid (AA). Increase in the oxidation current response with a negative shift of the anodic peak potential was observed at the cationic PDMA film-coated BDD (PDMA|BDD) electrode, compared with that at the bare BDD electrode. A more drastic enhancement in the oxidation peak current as well as more negative shift of oxidation potential was found at the ferrocyanide-trapped PDMA film-coated BDD ([Fe(CN)₆]^3−/4−|PDMA|BDD) electrode. This [Fe(CN)₆]^3−/4−|PDMA|BDD electrode can be used as an amperometric sensor of AA. Ferrocyanide, electrostatically trapped in the polymer film shows more electrocatalytic activity than that coordinatively attached to the polymer film or dissolved in the solution phase. The electrocatalytic current depends on the surface coverage of ferricyanide, Γ_Fe, within the polymer film. Diffusion coefficient (D) of AA in the solution was estimated by rotating disk electrode voltammetry: D = (5.8 ± 0.3) × 10⁻⁶ cm² s⁻¹. The second-order rate constant for the catalytic oxidation of AA by ferricyanide was also estimated to be 9.0 × 10⁴ M⁻¹ s⁻¹. In the hydrodynamic amperometry using the [Fe(CN)₆]^3−/4−|PDMA|BDD electrode, a successive addition of 1 μM AA caused the successive increase in current response with equal amplitude and the sensitivity was calculated as 0.233 μA cm⁻² μM⁻¹.     

Determination of trace selenium on hanging copper amalgam drop electrode

Hanging copper amalgam drop electrode has been applied for trace determination of selenium by cathodic stripping analysis. Detection limit for Se(IV) as low as 0.25 nM (0.02 μg L⁻¹) at deposition time (120 s) could be obtained. For seven successive determinations of Se(IV) at concentration of 5 nM relative standard deviation was 2.3% (n = 7). Interferences from selected metals and surfactant substances were examined. Absence of copper ions in sample solution causes easier optimization and makes method less vulnerable on contamination. The developed method was validated by analysis of certified reference materials (BCRs) and applied to selenium determinations in natural water samples, snow, mushrooms and ox liver.     

Microsomal cytochrome P450-3A4 (CYP3A4) nanobiosensor for the determination of 2,4-dichlorophenol—An endocrine disruptor compound

Cytochrome P450-3A4 (CYP3A4) is a monooxygenase enzyme that plays a major role in the detoxification of bioactive compounds and hydrophobic xenobiotics (e.g. medicines, drugs, environmental pollutants, food supplements and steroids). Physiologically the monooxygenation reactions of this class II, microsomal, b-type heme enzyme, usually requires cytochrome P450 reductase, NADPH. A novel CYP3A4 biosensor system that essentially simplified the enzymatic redox processes by allowing electron transfer between the electrode and the enzyme redox centre to occur, without any need for the physiological redox partners, was developed for the detection of 2,4-dichlorophenol (2,4-DCP), a priority environmental pollutant and an endocrine disruptor. The biosensor, GC/Naf-Co(Sep)³⁺/CYP3A4/Naf, was constructed by encapsulating CYP3A4 in a Nafion-cobalt (III) sepulchrate (Naf-Co(Sep)³⁺) composite film on a glassy carbon (GC) electrode. The responses of the biosensor to 2,4-dichlorophenol, erythromycin (CYP3A4 native substrate) and ketoconazole (CYP 3A4 natural inhibitor) were studied by cyclic and square wave voltammetric techniques. The detection limit (DL) of the biosensor for 2,4-dichlorophenol was 0.043 μg L⁻¹, which is by an order of magnitude lower than the EU limit (0.3 μg L⁻¹) for any pesticide compound in ground water. The biosensor's DL is lower than the U.S. Environmental Protection Agency's drinking water equivalent level (DWEL) value for 2,4-DCP, which is 2 μg L⁻¹.     

Modification of glassy carbon electrode with multi-walled carbon nanotubes and iron(III)-porphyrin film: Application to chlorate, bromate and iodate detection

In this study, multi-wall carbon nanotubes (MWCTs) is evaluated as a transducer, stabilizer and immobilization matrix for the construction of amperometric sensor based on iron-porphyrin. 5,10,15,20-Tetraphenyl-21H,23H-porphine iron(III) chloride (Fe(III)P) adsorbed on MWCNTs immobilized on the surface of glassy carbon electrode. Cyclic voltammograms of the Fe(III)P-incorporated-MWCNTs indicate a pair of well-defined and nearly reversible redox couple with surface confined characteristics at wide pH range (2-12). The surface coverage (Γ) and charge transfer rate constant (k_s) of Fe(III)P immobilized on MWCNTs were 7.68 × 10⁻⁹ mol cm⁻² and 1.8 s⁻¹, respectively, indicating high loading ability of MWCNTs for Fe(III)P and great facilitation of the electron transfer between Fe(III)P and carbon nanotubes immobilized on the electrode surface. Modified electrodes exhibit excellent electrocatalytic activity toward reduction of ClO₃⁻, IO₃⁻ and BrO₃⁻ in acidic solutions. The catalytic rate constants for catalytic reduction of bromate, chlorate and iodate were 6.8 × 10³, 7.4 × 10³ and 4.8 × 10² M⁻¹ s⁻¹, respectively. The hydrodynamic amperometry of rotating-modified electrode at constant potential versus reference electrode was used for detection of bromate, chlorate and iodate. The detection limit, linear calibration range and sensitivity for chlorate, bromate and iodate detections were 0.5 μM, 2 μM to 1 mM, 8.4 nA/μM, 0.6 μM, 2 μM to 0.15 mM, 11 nA/μM, and 2.5 μM, 10 μM to 4 mM and 1.5 nA/μM, respectively. Excellent electrochemical reversibility of the redox couple, good reproducibility, high stability, low detection limit, long life time, fast amperometric response time, wide linear concentration range, technical simplicity and possibility of rapid preparation are great advantages of this sensor. The obtained results show promising practical application of the Fe(III)P-MWCNTs-modified electrode as an amperometric sensor for chlorate, iodate and bromate detections.     

An electroanalytical application of 2-aminothiazole-modified silica gel after adsorption and separation of Hg(II) from heavy metals in aqueous solution

2-Aminothiazole covalently attached to a silica gel surface was prepared in order to obtain an adsorbent for Hg(II) ions having the following characteristics: good sorption capacity, chemical stability under conditions of use, and, especially, high selectivity. The accumulation voltammetry of mercury(II) was investigated at a carbon paste electrode chemically modified with silica gel functionalized with 2-aminothiazole (SIAMT-CPE). The repetitive cyclic voltammogram of mercury(II) solution in the potential range −0.2 to +0.6 V versus Ag/AgCl (0.02 mol L⁻¹ KNO₃; v=20 mV s−1) show two peaks one at about 0.1 V and other at 0.205 V. The anodic wave peak at 0.205 V is well defined and does not change during the cycles and it was therefore further investigated for analytical purposes using differential pulse anodic stripping voltammetry in differents supporting electrolytes. The mercury response was evaluated with respect to pH, electrode composition, preconcentration time, mercury concentration, “cleaning” solution, possible interferences and other variables. The precision for six determinations (n = 6) of 0.02 and 0.20 mg L⁻¹ Hg(II) was 4.1 and 3.5% (relative standard deviation), respectively. The detection limit was estimated as 0.10 μg L⁻¹ mercury(II) by means of 3:1 current-to-noise ratio in connection with the optimization of the various parameters involved and using the highest-possible analyser sensitivity.     

Development of a sensor based on tetracyanoethylenide (LiTCNE)/poly-l-lysine (PLL) for dopamine determination

The catalytic oxidation of dopamine (DA) at a LiTCNE (lithium tetracyanoethylenide) film modified electrode is studied by electrochemical approaches. The immobilization of LiTCNE was performed by a polymer (poly-l-lysine) to prepare this modified electrode and its application for dopamine (DA) determination is described in detail. The modified electrode showed a high activity for the electrooxidation of dopamine (DA) at E_p = 0.20 V versus SCE. The modified electrode presented a wide linear response range for DA from 0.01 up to 10 μmol l⁻¹ by differential pulse voltammetry (DPV) with a detection limit of 0.5 nmol l⁻¹. The repeatability of the proposed sensor evaluated in term of relative standard deviation was 3.2% for n = 10. The sensor was applied for the determination of dopamine in pharmaceutical formulations and the average recovery for these samples was 101.9 (±0.1)%.     

An electrochemical methanol sensor based on a Pd-Ni/SiNWs catalytic electrode

A novel electrochemical methanol sensor based on a catalytic electrode of palladium-nickel/silicon nanowires (Pd-Ni/SiNWs) is presented in this paper. Scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and electrochemical methods are employed to investigate the Pd-Ni/SiNWs electrode materials. These nanocomposite materials exhibit a highly ordered, wire-like structure with a wire length of ∼50 μm and a wire diameter ranging from 100 to 300 nm. The substrate has good electrocatalytic activity towards the oxidation of methanol in alkaline solutions. The performances of the prototype sensor are characterized by cyclic voltammetry and fixed potential amperometry techniques. In a 1 mol L⁻¹ KOH solution containing different methanol concentrations, the sensor exhibits a good sensitivity of 1.96 mA mmol⁻¹ L cm⁻² with R² = 0.99 and the corresponding detection limit of 18 μmol L⁻¹ (signal-to-noise ratio = 3, S/N = 3) for cyclic voltammetry. Meanwhile, the electrode also displays a sensitivity of 0.48 mA mmol⁻¹ L cm⁻² with R² = 0.98 and the corresponding detection limit of 25 μmol L⁻¹ (S/N = 3) for a fixed potential amperometry at −0.3 V versus an Ag/AgCl reference electrode. The results demonstrate that the Pd-Ni/SiNWs catalytic electrode has potential as an efficient and integrated sensor for methanol detection.     

Lithographically fabricated disposable bismuth-film electrodes for the trace determination of Pb(II) and Cd(II) by anodic stripping voltammetry

This work reports the photolithographic fabrication of disposable bismuth-film electrodes (BiFEs) using a thin-film deposition approach. The deposition of the bismuth layer was carried out by sputtering of metallic bismuth on a silicon substrate while the exact geometry of the BiFEs was produced by photolithography. The utility of these sensors was tested for the simultaneous trace determination of Cd(II) and Pb(II) by square wave anodic stripping voltammetry (SWASV). Using the selected conditions, the limits of detection were 0.5 μg l⁻¹ for Pb(II) and 1 μg l⁻¹ for Cd(II) at a preconcentration time of 4 min. The interference caused by Cu(II) was alleviated by the addition of ferrocyanide in the sample solution. Finally, the proposed BiFEs were successfully applied to the determination of Cd and Pb in a phosphate fertilizer and a river water sample. These sensors offer wide scope for trace metal analysis in terms of mass-production of mercury-free disposable sensors with performance comparable to their mercury counterparts.     

Electrocatalytic oxidation of deoxyguanosine on a glassy carbon electrode modified with a ruthenium oxide hexacyanoferrate film

The electrocatalytic oxidation of deoxyguanosine on a ruthenium hexacyanoferrate (RuOHCF) glassy carbon (GC) modified electrode was investigated in acid medium by using rotating disc electrode (RDE) voltammetry. Chronoamperometric experiments allowed information on the charge transport rate through the RuOHCF film and at a very short time window a diffusion-like behavior was observed with a D_ct value of 2.7 × 10⁻¹¹ cm² s⁻¹ for a film with Γ = 4.47 × 10⁻⁹ mol cm⁻². The influence of systematic variation of rotation rate, film thickness and the electrode potential indicates that the rate of cross-chemical reaction between Ru(IV) centers immobilized into the film and deoxyguanosine controls the overall electrodic process and the value of the rate constant was found to be 3.2 × 10⁶ mol⁻¹ L¹ s⁻¹. The relatively high rate constant of the cross-reaction, the facile penetration of the substrate through the film and the fast transport of electrons suggest that the electrocatalytic process occurs throughout the film layer.