Selective method for the determination of gold by anodic stripping voltammetry

A highly selective method for the deter- mination of gold by anodic stripping voltammetry is described. For preconcentration a glassy carbon electrode, activated by deposition of small amounts of gold before the measurement, is proposed. The Au³⁺ reduction process at such an electrode is effective starting with the potential +0.4 V vs. Ag/AgCl electrode. A linear dependence of the current of the gold stripping peak on the gold concentration was obtained in the range from 5×10^–8 to 1×10^–6 mol/l. The relative standard deviation for 2×10^-7 mol/l HAuCl₄ was 4.2% (n=5). The detection limit was 4×10^-9 mol/l. The accuracy of the method was verified by the determination of gold in reference materials.     

Simultaneous determination of Mn(II), Cu(II) and Fe(III) as 2-(5′-bromo-2′-pyridylazo)-5-diethylaminophenol complexes by adsorptive cathodic stripping voltammetry at a carbon paste electrode

A simple and precise square-wave adsorptive cathodic stripping voltammetry (SW-AdCSV) method has been described for simultaneous determination of Mn(II), Cu(II) and Fe(III) in water samples using a carbon paste electrode. In 0.1 mol L⁻¹ acetate buffer (pH 5) containing 50 μmol L⁻¹ of 2-(5′-bromo-2′-pyridylazo)-5-diethylaminophenol (5-Br-PADAP), Mn(II), Cu(II) and Fe(III) were simultaneously determined as metal-complexes with 5-Br-PADAP following preconcentration onto the carbon paste electrode by adsorptive accumulation at +1.0 V (vs. Ag/AgCl/3 M KCl). Insignificant interference from various cations (K⁺, Na⁺, Mg²⁺, Ca²⁺, Al³⁺, Bi³⁺, Sb³⁺, Se⁴⁺, Zn²⁺, Ni²⁺, Co²⁺, Cd²⁺, Pb²⁺, V⁵⁺, Ti⁴⁺ and NH₄⁺), anions (HCO₃⁻, Cl⁻, NO³⁻, SO₄²⁻ and PO₄³⁻) and ascorbic acid was noticed. Limits of detection of 0.066, 0.108 and 0.093 μg L⁻¹ and limits of quantitation of 0.22, 0.36 and 0.31 μg L⁻¹ Mn(II), Cu(II) and Fe(III), respectively, were achieved by the described method. The described stripping voltammetry method was successfully applied for simultaneous determination of Mn(II), Cu(II) and Fe(III) in ground, tap and bottled natural water samples.     

Silver nanoparticle assemblies supported on glassy-carbon electrodes for the electro-analytical detection of hydrogen peroxide

Electrochemical detection of hydrogen peroxide using an edge-plane pyrolytic-graphite electrode (EPPG), a glassy carbon (GC) electrode, and a silver nanoparticle-modified GC electrode is reported. It is shown, in phosphate buffer (0.05 mol L^–1, pH 7.4), that hydrogen peroxide cannot be detected directly on either the EPPG or GC electrodes. However, reduction can be facilitated by modification of the glassy-carbon surface with nanosized silver assemblies. The optimum conditions for modification of the GC electrode with silver nanoparticles were found to be deposition for 1 min at –0.5 V vs. Ag from 5 mmol L^–1 AgNO₃/0.1 mol L^–1 TBAP/MeCN, followed by stripping for 2 min at +0.5 V vs. Ag in the same solution. A wave, due to the reduction of hydrogen peroxide on the silver nanoparticles is observed at –0.68 V vs. SCE. The limit of detection for this modified nanosilver electrode was 2.0×10^–6 mol L^–1 for hydrogen peroxide in phosphate buffer (0.05 mol L^–1, pH 7.4) with a sensitivity which is five times higher than that observed at a silver macro-electrode. Also observed is a shoulder on the voltammetric wave corresponding to the reduction of oxygen, which is produced by silver-catalysed chemical decomposition of hydrogen peroxide to water and oxygen then oxygen reduction at the surface of the glassy-carbon electrode.     

Bifunctional polydopamine@Fe3O4 core–shell nanoparticles for electrochemical determination of lead(II) and cadmium(II)

The present paper has focused on the potential application of the bifunctional polydopamine@Fe₃O₄ core–shell nanoparticles for development of a simple, stable and highly selective electrochemical method for metal ions monitoring in real samples. The electrochemical method is based on electrochemical preconcentration/reduction of metal ions onto a polydopamine@Fe₃O₄ modified magnetic glassy carbon electrode at −1.1 V (versus SCE) in 0.1 M pH 5.0 acetate solution containing Pb²⁺ and Cd²⁺ during 160 s, followed by subsequent anodic stripping. The proposed method has been demonstrated highly selective and sensitive detection of Pb²⁺ and Cd²⁺, with the calculated detection limits of 1.4 × 10⁻¹¹ M and 9.2 × 10⁻¹¹ M. Under the optimized conditions, the square wave anodic stripping voltammetry response of the modified electrode to Pb²⁺ (or Cd²⁺) shows a linear concentration range of 5.0–600 nM (or 20–590 nM) with a correlation coefficient of 0.997 (or 0.994). Further, the proposed method has been performed to successfully detect Pb²⁺ and Cd²⁺ in aqueous effluent.     

Highly sensitive determination of mercury using copper enhancer by diamond electrode coupled with sequential injection–anodic stripping voltammetry

A highly sensitive determination of mercury in the presence of Cu(II) using a boron-doped diamond (BDD) thin film electrode coupled with sequential injection–anodic stripping voltammetry (SI–ASV) was proposed. The Cu(II) was simultaneously deposited with Hg(II) in a 0.5 M HCl supporting electrolyte by electrodeposition. In presence of an excess of Cu(II), the sensitivity for the determination of Hg(II) was remarkably enhanced. Cu(II) and Hg(II) were on-line deposited onto the BDD electrode surface at −1.0 V (vs. Ag/AgCl, 3 M KCl) for 150 s with a flow rate of 14 μL s⁻¹. An anodic stripping voltammogram was recorded from −0.4 V to 0.25 V using a frequency of 60 Hz, an amplitude of 50 mV, and a step potential of 10 mV at a stopped flow. Under the optimal conditions, well-defined peaks of Cu(II) and Hg(II) were found at −0.25 V and +0.05 V (vs. Ag/AgCl, 3 M KCl), respectively. The detection of Hg(II) showed two linear dynamic ranges (0.1–30.0 ng mL⁻¹ and 5.0–60.0 ng mL⁻¹). The limit of detection (S/N = 3) obtained from the experiment was found to be 0.04 ng mL⁻¹. The precision values for 10 replicate determinations were 1.1, 2.1 and 2.9% RSD for 0.5, 10 and 20 ng mL⁻¹, respectively. The proposed method has been successfully applied for the determination of Hg(II) in seawater, salmon, squid, cockle and seaweed samples. A comparison between the proposed method and an inductively coupled plasma optical emission spectrometry (ICP-OES) standard method was performed on the samples, and the concentrations obtained via both methods were in agreement with the certified values of Hg(II), according to the paired t-test at a 95% confidence level.     

方波伏安法测定酚酞片含量

研究了酚酞在0.5 mol/L氨水-氯化铵缓冲溶液(pH 10)介质中汞膜电极上的电化学行为,并依此建立了酚酞含量的方波伏安法测定.酚酞于-0.98 V(VS.Ag/AgCl)处出现一灵敏的阴极还原峰,峰高与酚酞的浓度在3.0×10-7-5.0×10-5mol/L范围内有良好的线性关系.方法的最低检出限为1.0×10-7mol/L,方法用于酚酞片中酚酞含量的测定,结果满意.     

Selective method for the determination of gold by anodic stripping voltammetry

A highly selective method for the deter- mination of gold by anodic stripping voltammetry is described. For preconcentration a glassy carbon electrode, activated by deposition of small amounts of gold before the measurement, is proposed. The Au³⁺ reduction process at such an electrode is effective starting with the potential +0.4 V vs. Ag/AgCl electrode. A linear dependence of the current of the gold stripping peak on the gold concentration was obtained in the range from 5×10⁻⁸ to 1×10⁻⁶ mol/l. The relative standard deviation for 2×10^-7 mol/l HAuCl₄ was 4.2% (n=5). The detection limit was 4×10^-9 mol/l. The accuracy of the method was verified by the determination of gold in reference materials.     

Square-wave voltametric method for determination of molinate concentration in a biological process using a hanging mercury drop electrode

A square-wave voltammetric (SWV) method using a hanging mercury drop electrode (HMDE) has been developed for determination of the herbicide molinate in a biodegradation process. The method is based on controlled adsorptive accumulation of molinate for 10 s at a potential of –0.8 V versus AgCl/Ag. An anodic peak, due to oxidation of the adsorbed pesticide, was observed in the cyclic voltammogram at ca. –0.320 V versus AgCl/Ag; a very small cathodic peak was also detected. The SWV calibration plot was established to be linear in the range 5.0×10^–6 to 9.0×10^–6 mol L^–1; this corresponded to a detection limit of 3.5×10^–8 mol L^–1. This electroanalytical method was used to monitor the decrease of molinate concentration in river waters along a biodegradation process using a bacterial mixed culture. The results achieved with this voltammetric method were compared with those obtained by use of a chromatographic method (HPLC–UV) and no significant statistical differences were observed.     

Electrochemical determination of Cd<Superscript>2+</Superscript> at a titanium electrode modified with a lead film by square wave anodic stripping voltammetry

The modified titanium electrode with lead film (PbTiE) was used for determination of trace levels of cadmium using square wave anodic stripping voltammetry (SWASV). The measurement of cadmium on the PbTiE has the best reply under the following conditions of PbTiE preparation: 10^–3 mol L^–1 Pb²⁺ in HCl (pH 1.0), deposition potential of–1.40 V vs. Ag/AgCl/KCl_sat and deposition time of 300 s. The PbTiE reveals highly linear behavior in the concentration range 5 × 10^–8 to 10^–6 mol L^–1, with a limit of detection of 2 × 10^–9 mol L^–1. Interference of nine ionic species was evaluated. The measurements were carried out without removing dissolved oxygen from the solution.     

Electrochemiluminescent behaviors of alkaloids and tris(2,2'-bipyridine) ruthenium in organically modified silicate film

Electrogenerated chemiluminescences (ECLs) of alkaloids, such as berberine, trigonelline, allantoin and betaine, were studied in an aqueous alkaline buffer solution (pH 9.5), based on tris(2,2′-bipyridine)ruthenium(II) [Ru(bpy)₃²⁺] immobilized in organically modified silicates (ORMOSILs) film on a glassy carbon electrode (GCE). The immobilized Ru(bpy)₃²⁺ showed good electrochemical and photochemical activities. In a flow system, the eluted alkaloids were oxidized on the modified GCE, and reacted with immobilized Ru(bpy)₃²⁺ at the potential of +1.50 V (versus Ag/AgCl). The luminescence with λ_max 610 nm was caused by a reaction of electrolytically formed Ru(bpy)₃³⁺ with an oxidized amine group to generate Ru(bpy)₃^2+*. The determination limit was 5 × 10⁻⁶ mol L⁻¹, 8 × 10⁻⁶ mol L⁻¹, 2.0 × 10⁻⁵ mol L⁻¹ and 5.0 × 10⁻⁵ mol L⁻¹ for berberine, trigonelline, allantoin and betaine at S/N 3, respectively. In addition, the factors affecting the determination of the four alkaloids were also studied.     

Adsorptive stripping voltammetric determination of trace concentrations of molybdenum at an in situ plated lead film electrode

An in situ plated lead film electrode has been applied for adsorptive stripping voltammetric determination of trace concentrations of molybdenum in the presence of Alizarin S. The procedure is based on the preconcentration of the molybdenum-Alizarin S complex at an in situ plated lead film electrode held at −0.6 V (versus Ag/AgCl), followed by a negatively sweeping square wave voltammetric scan. The peak current is proportional to the concentration of molybdenum over the range 2 × 10⁻⁹ to 5 × 10⁻⁸ mol L⁻¹, with a 3σ detection limit of 9 × 10⁻¹⁰ mol L⁻¹ with an accumulation time of 60 s. The measurements were carried out from underaerated solutions. The proposed procedure was validated in the course of Mo(VI) determination in water certified reference materials.     

Synergy between Printex nano-carbons and silver nanoparticles for sensitive estimation of antioxidant activity

We report on the synthesis, characterization and applications of a Printex L6 carbon-silver hybrid nanomaterial (PC-Ag), which was obtained using a polyol method. In addition, we also highlight the use of Printex L6 nano-carbon as a much cheaper alternative to the use of carbon nanotubes and graphene. The silver nanoparticles (AgNP) were prepared directly on the surface of the Printex 6L carbon “nanocarbon” material using ethylene glycol as the reducing agent. The hybrid nanomaterial was characterized by High-angle annular dark-field transmission electron microscopy (HAADF-TEM), energy–dispersive X-ray spectroscopy (EDX), selected area electron diffraction (SAED), Raman spectroscopy and cyclic voltammetry. Optimized electrocatalytic activity on glassy carbon electrode was reached for the architecture GC/PC-Ag, the silver nanoparticles with size ranging between 1 and 2 nm were well–distributed throughout the hybrid material. The synergy between PC nano-carbons and AgNPs was verified by detection of gallic acid (GA) at a low applied potential (0.091 V vs. Ag/AgCl). GA detection was performed in a concentration range between 5.0 × 10⁻⁷ and 8.5 × 10⁻⁶ mol L⁻¹, with a detection limit of 6.63 × 10⁻⁸ mol L⁻¹ (66.3 nmol L⁻¹), which is considerably lower than similar devices. The approach for fabricating the reproducible GC/PC-Ag electrodes is entirely generic and may be explored for other types of (bio)sensors and devices.     

Development and evaluation of a diffusive gradients in a thin film technique for measuring ammonium in freshwaters

A new diffusive gradients in a thin film (DGT) technique, using Microlite PrCH cation exchange resin, was developed and evaluated for measuring NH₄–N in freshwaters. Microlite PrCH had high uptake (>92.5%) and elution efficiencies (87.2% using 2 mol L⁻¹ NaCl). Mass vs. time validation experiments over 24 h demonstrated excellent linearity (R² ≥ 0.996). PrCH-DGT binding layers had an extremely high intrinsic binding capacity for NH₄–N (∼3000 μg). NH₄–N uptake was quantitative over pH ranges 3.5–8.5 and ionic strength (up to 0.012 mol L⁻¹ as NaCl) typical of freshwater systems. Several cations (Na⁺, K⁺, Ca²⁺ and Mg²⁺) were found to compete with NH₄–N for uptake by PrCH-DGT, but NH₄–N uptake was quantitative over concentration ranges typical of freshwater (up to 0.012 mol L⁻¹ Na⁺, 0.006 mol L⁻¹ K⁺, 0.003 mol L⁻¹ Ca²⁺ and 0.004 mol L⁻¹ Mg²⁺). Effective diffusion coefficients determined from mass vs. time experiments changed non-linearly with electrical conductivity. Field deployments of DGT samplers with varying diffusive layer thicknesses validated the use of the technique in situ, allowed deployment times to be manipulated with respect to NH₄–N concentration, and enable the calculation of the diffusive boundary layer thickness. Daily grab sample NH₄–N concentrations were observed to vary considerably independent of major rainfall events, but good agreements were obtained between PrCH-DGT values and mean grab sample measurements of NH₄–N (C_DGT:C_SOLN 0.83–1.3). Reproducibility of DGT measurements in the field was good (relative standard deviation < 11%). Limit of detection was 0.63 μg L⁻¹ (equivalent to 0.045 μmol L⁻¹) based on 24 h deployments.     

Determination of medecamycin by adsorptive stripping voltammetry with an activated electrode

The adsorptive and electrochemical behaviors of medecamycin were investigated on a glassy carbon electrode (GCE) pretreated by anodic oxidation at +1.8 V for 5 min in 0.025 mol l^–1 NH₃-NH₄Cl (pH 8.6) solution. An adsorptive stripping voltammetric method for the determination of medecamycin at the pretreated glassy carbon electrode has been developed. Medecamycin was accumulated in NH₃-NH₄Cl buffer (pH 9.0) at a potential of –0.7 V (vs. saturated calomel electrode (SCE)) for a certain time, and then determined by second-order differential anodic stripping voltammetry. The second-order differential anodic stripping peak current at +0.72 V was proportional to the concentration of medecamycin in the range 2.0 g ml^–1 to 50.0 g ml^–1. The detection limit (three times the signal-to-noise) was 1.0 g ml^–1 and the relative standard deviation of the results was 3.28% for eight successive determinations of 10.0 g ml^–1 medecamycin. This method has been applied to the direct determination of medecamycin in commercial tablets and spiked urine samples with satisfactory results.     

Study on the Electrochemical Behavior of Melatonin with an Activated Electrode

It was found that melatonin could be incorporated and accumulated on the surface of the glassy carbon electrode which was activated electrochemically by pretreatment in sodium hydroxide solution by means of cycling the potential well into the positive limit of the solvent. In Britton‐Robinson buffer solution (pH 6.7), melatonin gave a sensitive oxidation wave at a potential of +0.65 V (vs.Ag/AgCl) by using Osteryoung square‐wave stripping voltammetry (OSWSV). The oxidation process has been shown to be irreversible and adsorption‐controlled at this electrode by means of cyclic voltammetry and linear sweep voltammetry. A chronocoulometric characterization of the adsorption characteristics of melatonin at this electrode is also presented. The factors affecting the peak current were optimized, and the dependence of peak currents on the concentration of melatonin was found to be linear in the range 8.0×10^?7?1.0×10^?5 mol L^?1. A detection limit of 5.0×10^?8 mol L^?1 was obtained (signal‐to‐noise ratio of 3). This method was applied to the assay of melatonin in tablets and capsules with good recoveries (98–100%).     

Mercury-free simultaneous determination of cadmium and lead at a glassy carbon electrode modified with multi-wall carbon nanotubes

A multi-wall carbon nanotube (MWNT) modified glassy carbon electrode (GCE) was described for the simultaneous determination of trace levels of cadmium and lead by anodic stripping voltammetry (ASV). In pH 4.5 NaAc-HAc buffer containing 0.02 mol/l KI, Cd²⁺ and Pb²⁺ first adsorb onto the surface of a MWNT film coated GCE and then reduce at −1.20 V. During the positive potential sweep, reduced cadmium and lead were oxidized, and two well-defined stripping peaks appeared at −0.88 and −0.62 V. Compared with a bare GCE, a MWNT film coated GCE greatly improves the sensitivity of determining cadmium and lead. Low concentration of I⁻ significantly enhances the stripping peak currents since it induces Cd²⁺ and Pb²⁺ to adsorb at the electrode surface. The striping peak currents change linearly with the concentration of Cd²⁺ from 2.5×10⁻⁸ to 1×10⁻⁵ mol/l and with that of Pb²⁺ from 2×10⁻⁸ to 1×10⁻⁵ mol/l. The lowest detectable concentrations of Cd²⁺ and Pb²⁺ are estimated to be 6×10⁻⁹ and 4×10⁻⁹ mol/l, respectively. The high sensitivity, selectivity, and stability of this MWNT film coated electrode demonstrated its practical application for a simple, rapid and economical determination of trace levels of Cd²⁺ and Pb²⁺ in water samples.     

Determination of Blasticidin S in Spiked Rice Using SW Voltammetry with a Renewable Silver Amalgam Film Electrode

Blasticidin S (BS) was determined in spiked rice samples by square wave voltammetry (SWV) and square wave stripping voltammetry (SWSV) using a cyclic renewable silver amalgam film electrode (Hg(Ag)FE). It was found that the compound can act as an electrocatalyst. In Britton? Robinson buffer at pH 7.0 a signal connected with the hydrogen evolution reaction was detected at ?1.2 V versus Ag/AgCl. Validation of the method was carried out. The detection and quantification limits were found to be 2.13×10^?8 mol L^?1; 7.10×10^?8 mol L^?1 for SWV and 2.65×10^?9 mol L^?1; 8.85×10^?9 mol L^?1 for SWSV, respectively.     

Determination of Aldehydes and Ketones in Fuel Ethanol by High-Performance Liquid Chromatography with Electrochemical Detection

A new methodology was developed for analysis of aldehydes and ketones in fuel ethanol by high-performance liquid chromatography (HPLC) coupled to electrochemical detection. The electrochemical oxidation of 5-hydroxymethylfurfural, 2-furfuraldehyde, butyraldehyde, acetone and methyl ethyl ketone derivatized with 2,4-dinitrophenylhydrazine (DNPH) at glassy carbon electrode present a well defined wave at +0.94 V; +0.99 V; +1.29 V; +1.15 V and +1.18 V, respectively which are the basis for its determination on electrochemical detector. The carbonyl compounds derivatized were separated by a reverse-phase column under isocratic conditions with a mobile phase containing a binary mixture of methanol / LiClO_4(aq) at a concentration of 1.0 × 10⁻³ mol L⁻¹ (80:20 v/v) and a flow-rate of 1.1mL min⁻¹ . The optimum potential for the electrochemical detection of aldehydes-DNPH and ketones-DNPH was +1.0 V vs. Ag/AgCl. The analytical curve of aldehydes-DNPH and ketones-DNPH presented linearity over the range 5.0 to 400.0 ng mL⁻¹, with detection limits of 1.7 to 2.0 ng mL⁻¹ and quantification limits from 5.0 to 6.2 ng mL⁻¹, using injection volume of 20 μL. The proposed methodology was simple, low time-consuming (15 min/analysis) and presented analytical recovery higher than 95%.     

硒碳糊电极微分电位溶出法测定铜和铋

建立了掺杂硒碳糊电极同时测定铜和铋的微分电位溶出法。在HCl(0.05mol/L)中,在-0.3V(vs.Ag/AgCl)下,Cu2+和Bi3+电沉积在电极表面,再在溶液中溶解氧的作用下,铜和铋从电极表面溶出,分别于0.30V和0.02V获得灵敏的电位溶出峰。微分电位溶出峰高(dt/dE)与铜和铋的浓度成线性关系,线性范围为5.0×10-9～1.55×10-7mol/L,检出限分别为4.0×10-9和2.5×10-9mol/L(S/N=3)。方法用于实际样品中铜和铋的测定,结果令人满意。     

Simultaneous determination of lead(II) and cadmium(II) at a diacetyldioxime modified carbon paste electrode by differential pulse stripping voltammetry

A simple and effective chemically modified carbon paste electrode (CMCPE) for the simultaneous determination of lead(II) and cadmium(II) was developed in this work. The electrode was prepared by the addition of diacetyldioxime into a carbon paste mixture. Pb²⁺ and Cd²⁺ were preconcentrated on the surface of the modified electrode by complexing with diacetyldioxime and reduced at a negative potential (−1.10 V). Then the reduced products were oxidized by differential pulse stripping. The fact that two stripping peaks appeared on the voltammograms at the potentials of −0.65 V (Cd²⁺) and −0.91 V (Pb²⁺) demonstrates the possibility of simultaneous determination of Pb²⁺ and Cd²⁺. Under the optimized working conditions, calibration graphs were linear in the concentration ranges of 1.0×10⁻⁷-1.5×10⁻⁵ mol l⁻¹ (Pb²⁺) and 2.5×10⁻⁷-2.5×10⁻⁵ mol l⁻¹ (Cd²⁺), respectively. For 5 min preconcentration, detection limits of 1×10⁻⁸ mol l⁻¹ (Pb²⁺) and 4×10⁻⁸ mol l⁻¹ (Cd²⁺) were obtained at the signal noise ratio (SNR) of 3. To evaluate the reproducibility of the newly developed electrode, the measurements of 5×10⁻⁷ mol l⁻¹ Pb²⁺ and Cd²⁺ were parallel carried out for six times at different electrodes and the relative standard deviations were 2.9% (Pb²⁺) and 3.2% (Cd²⁺), respectively. Interferences by some metals were investigated. Only Ni²⁺ and Hg²⁺ apparently affected the peak currents of Pb²⁺ and Cd²⁺. The diacetyldioxime modified carbon paste electrode was applied to the determination of Pb²⁺ and Cd²⁺ in water samples. The results indicate that this electrode is sensitive and effective for the simultaneous determination of Pb²⁺ and Cd²⁺.