Electroanalytical characteristics of antipsychotic drug ziprasidone and its determination in pharmaceuticals and serum samples on solid electrodes

Ziprasidone is a psychotropic agent used for the treatment of schizophrenia. Its oxidation was investigated electrochemically at boron-doped diamond and glassy carbon electrodes using cyclic, differential pulse, and square wave voltammetry. The dependence of the peak current and peak potentials on pH, concentration, nature of the buffer, and scan rate were examined. The process was diffusion and adsorption controlled for boron-doped diamond and glassy carbon electrodes, respectively. The possible mechanism of oxidation was discussed with some model compounds that have indole and piperazine oxidations. A linear response was obtained between 8 × 10⁻⁷ and 8 × 10⁻⁵ M for the first peak in acetate buffer (pH 5.5) and between 2 × 10⁻⁶ and 2 × 10⁻⁴ M for the second peak in 0.1 M H₂SO₄ with boron-doped diamond electrode for differential pulse and square wave voltammetric techniques. The reproducibility and accuracy of the proposed methods were found between 0.31 and 1.20, 99.27 and 100.22, respectively. The recovery studies were also achieved to check selectivity and accuracy of the methods. The proposed methods were applied for the determination of ziprasidone from pharmaceutical dosage forms and human serum samples without any time-consuming extraction, separation, evaporation or adsorption steps prior to drug assay except precipitation of the proteins using acetonitrile. The results were statistically compared with those obtained through an established LC-UV technique, no significant differences were been found between the voltammetric and LC methods.     

Flower-like self-assembly of gold nanoparticles for highly sensitive electrochemical detection of chromium(VI)

We report here the fabrication of a flower-like self-assembly of gold nanoparticles (AuNPs) on a glassy carbon electrode (GCE) as a highly sensitive platform for ultratrace Cr(VI) detection. Two AuNP layers are used in the current approach, in which the first is electroplated on the GCE surface as anchors for binding to an overcoated thiol sol–gel film derived from 3-mercaptopropyltrimethoxysilane (MPTS). The second AuNP layer is then self-assembled on the surface of the sol–gel film, forming flower-like gold nanoelectrodes enlarging the electrode surface. When functionalized by a thiol pyridinium, the fabricated electrode displays a well-defined peak for selective Cr(VI) reduction with an unusually large, linear concentration range of 10–1200 ng L⁻¹ and a low detection limit of 2.9 ng L⁻¹. In comparison to previous approaches using MPTS and AuNPs on Au electrodes, the current work expands the use of AuNPs to the GCE. Subsequent functionalization of the secondary AuNPs by a thiol pyridinium and adsorption/preconcentration of Cr(VI) lead to the unusually large detection range and high sensitivity. The stepwise preparation of the electrode has been characterized by electrochemical impedance spectroscopy (EIS), scanning electronic microscopy (SEM), and IR. The newly designed electrode exhibits good stability, and has been successfully employed to measure chromium in a pre-treated blood sample. The method demonstrates acceptable fabrication reproducibility and accuracy.     

Hexavalent Chromium Reduction by Free and Immobilized Cell-free Extract of <Emphasis Type="Italic">Arthrobacter rhombi-RE</Emphasis>

In the present study, hexavalent chromium (Cr(VI)) reduction potential of chromium reductase associated with the cell-free extracts (CFE) of Arthrobacter rhombi-RE species was evaluated. Arthrobacter rhombi-RE, an efficient Cr(VI) reducing bacterium, was enriched and isolated from a chromium-contaminated site. Chromium reductase activity of Arthrobacter rhombi-RE strain was associated with the cell-free extract and the contribution of extracellular enzymes to Cr(VI) reduction was negligible. NADH enhanced the chromium reductase activity. The enzyme activity was optimal at a pH of 5.5 and a temperature of 30 °C. Among the ten electron donors screened, sodium pyruvate was the most effective one followed by NADH and propionic acid. Michaelis–Menten constant, K _m, and maximum reaction rate, V _max, obtained from the Lineweaver–Burk plot were 48 μM and 4.09 nM/mg protein/min, respectively, in presence of NADH as electron donor and 170.5 μM and 4.29 nM/mg protein/min, respectively, in presence of sodium pyruvate as electron donor. Ca²⁺ enhanced the enzyme activity while Hg²⁺, Cd²⁺, Ba²⁺, and Zn²⁺ inhibited the enzyme activity. Among the various immobilization matrices screened, calcium alginate beads seemed to be the most effective one. Though immobilized enzyme system was able to reduce Cr(VI), the performance was not very encouraging in continuous mode of operation.     

Microwave activation of electrochemical processes: enhanced PbO2 electrodeposition, stripping and electrocatalysis

Microwave activation of electrochemical processes has recently been introduced as a new technique for the enhancement and control of processes at electrode|solution (electrolyte) interfaces. This methodology is extended to processes at glassy carbon and boron-doped diamond electrodes. Deposition of both Pb metal and PbO₂ from an aqueous solution of Pb²⁺ (0.1 M HNO₃) are affected by microwave radiation. The formation of PbO₂ on anodically pre-treated boron-doped diamond is demonstrated to change from kinetically sluggish and poorly defined at room temperature to nearly diffusion controlled and well defined in the presence of microwave activation. Calibration of the temperature at the electrode|solution (electrolyte) interface with the Fe^3+/2+ (0.1 M HNO₃) redox system allows the experimentally observed effects to be identified as predominantly thermal in nature and therefore consistent with a localized heating effect at the electrode|solution interface. The microwave-activated deposition of PbO₂ on boron-doped diamond remains facile in the presence of excess oxidizable organic compounds such as ethylene glycol. An increase of the current for the electrocatalytic oxidation of ethylene glycol at PbO₂/boron-doped diamond electrodes in the presence of microwave radiation is observed. Preliminary results suggest that the electrodissolution of solid microparticles of PbO₂ abrasively attached to the surface of a glassy carbon electrode is also enhanced in the presence of microwave radiation. Electronic Publication     

Polyethylenimine Functionalized Multi‐walled Carbon Nanotubes for Electrochemical Detection of Chromium(VI)

Multi‐walled carbon nanotubes (MWCNTs) functionalized with polyethylenimine (PEI) were synthesized and characterized by dispersibility, field‐emission scanning electron microscope (FE‐SEM), FT‐IR and thermogravimetric Analyzer (TGA). The glassy carbon electrodes modified by MWCNT‐PEI composite were used for sensitive and selective detection of chromium (VI). A linear response was obtained over a wide range of Cr(VI) concentrations (0.002–20 µmol L^?1) with the detection limit of 0.0006 µmol L^?1 (S/N=3). The proposed electrodes were used successfully for Cr(VI) detection in three real water samples.     

Electroanalytical Detection of Cr(VI) and Cr(III) Ions Using a Novel Microbial Sensor

A microbial sensor, namely carbon paste electrode (CPE) modified with Citrobacter freundii (Cf–CPE) has been developed for the detection of hexavalent (Cr(VI)) and trivalent (Cr(III)) chromium present in aqueous samples using voltammetry, an electroanalytical technique. The biosensor developed, demonstrated about a twofold higher performance as compared to the bare CPE for the chosen ions. Using cyclic voltammetry and by employing the fabricated Cf–CPE, the lowest limit of detection (LLOD) of 1x10⁻⁴ M and 5x10⁻⁴ M for Cr(VI) and Cr(III) ions respectively could be achieved. By adopting the Differential Pulse Cathodic Stripping Voltammetric technique, the LLOD could be further improved to 1x10⁻⁹ M and 1x10⁻⁷ M for Cr(VI) and Cr(III) ions respectively using the biomodified electrodes. The reactions occurring at the electrode surface‐chromium solution interface and the mechanisms of biosorption of chromium species onto the biosensor are discussed. The stability and utility of the developed biosensor for the analysis of Cr(VI) and Cr(III) ions in chromite mine water samples has been evaluated.     

Voltammetric study and electrochemical detection of hexavalent chromium at gold nanoparticle-electrodeposited indium tinoxide (ITO) electrodes in acidic media

The voltammetric behavior of hexavalent chromium species (Cr(VI)) was respectively studied at ITO, bulk Au, and Au-electrodeposited electrodes in 0.01 M NaCl aqueous solutions containing 0.01 M HCl. It was found that performance degradation of the ITO electrodes toward the reduction of Cr(VI) can be suppressed by modifying the electrode surface with gold nanoparticles (AuNPs), which were formed on ITO electrodes by potential-sweeping or potential-step electrodeposition in a 0.01 M Na(2)SO(4) solution containing 1 mM HAuCl(4) x 3 H(2)O and 0.01 M H(2)SO(4). After the modification, the surface of ITO electrodes turned to the characteristically red or blue color exhibited by AuNPs. The gold nanoparticle-electrodeposited indium-tinoxide electrode (AuNP-ITO) demonstrates unique catalytic behavior, higher sensitivity and stability in the reduction of Cr(VI). Cr(VI) species was detected by either cyclic voltammetry or hydrodynamic amperometry. By cyclic voltammetry, the dependence of cathodic peak current on concentration was linear from 5 to 100 microM with a detection limit of 2 microM (sigma=3), and linearity was obtained from 0.5 to 50 microM by hydrodynamic amperometry where a constant potential of +0.2V (vs. Ag/AgCl) was applied and a batch-injection cell was employed. For hydrodynamic amperometry, the detection limit was 0.1 microM (sigma=3).     

Electrochemical Determination of Anti-Hyperlipidemic Drug Ezetimibe Based on its Oxidation on Solid Electrodes

Ezetimibe is the first of a new class of drugs that selectively inhibits cholesterol absorption in the small intestine and reduces plasma LDL cholesterol. In this study, electrochemical oxidation of ezetimibe was investigated on carbon based electrodes and a single and irreversible peak at both electrodes was observed. A linear response was detected between 2 × 10^?6 and 8 × 10^?5 M with glassy carbon electrode and between 2 × 10^?6 and 2 × 10^?4 M with a boron-doped diamond electrode in 0.1 M H₂SO₄ supporting electrolyte. The proposed methods were successfully applied for the determination of ezetimibe from pharmaceutical dosage forms and human serum samples.     

Speciation of chromium using chronoamperometric biosensors based on screen-printed electrodes

Chronoamperometric assays based on tyrosinase and glucose oxidase (GOx) inactivation have been developed for the monitoring of Cr(III) and Cr(VI). Tyrosinase was immobilized by crosslinking on screen-printed carbon electrodes (SPCEs) containing tetrathiafulvalene (TTF) as electron transfer mediator. The tyrosinase/SPC_TTFE response to pyrocatechol is inhibited by Cr(III). This process, that is not affected by Cr(VI), allows the determination of Cr(III) with a capability of detection of 2.0 ± 0.2 μM and a reproducibility of 5.5%. GOx modified screen-printed carbon platinised electrodes (SPC_PtEs) were developed for the selective determination of Cr(VI) using ferricyanide as redox mediator. The biosensor was able to discriminate two different oxidation states of chromium being able to reject Cr(III) and to detect the toxic species Cr(VI). Chronoamperometric response of the biosensor towards glucose decreases with the presence of Cr(VI), with a capability of detection of 90.5 ± 7.6 nM and a reproducibility of 6.2%. A bipotentiostatic chronoamperometric biosensor was finally developed using a tyrosinase/SPC_TTFE and a GOx/SPC_PtE connected in array mode for the simultaneous determination of Cr(III) and Cr(VI) in spiked tap water and in waste water from a tannery factory samples.     

Electrochemical evaluation and determination of antiretroviral drug fosamprenavir using boron-doped diamond and glassy carbon electrodes

Fosamprenavir is a pro-drug of the antiretroviral protease inhibitor amprenavir and is oxidizable at solid electrodes. The anodic oxidation behavior of fosamprenavir was investigated using cyclic and linear sweep voltammetry at boron-doped diamond and glassy carbon electrodes. In cyclic voltammetry, depending on pH values, fosamprenavir showed one sharp irreversible oxidation peak or wave depending on the working electrode. The mechanism of the oxidation process was discussed. The voltammetric study of some model compounds allowed elucidation of the possible oxidation mechanism of fosamprenavir. The aim of this study was to determine fosamprenavir levels in pharmaceutical formulations and biological samples by means of electrochemical methods. Using the sharp oxidation response, two voltammetric methods were described for the determination of fosamprenavir by differential pulse and square-wave voltammetry at the boron-doped diamond and glassy carbon electrodes. These two voltammetric techniques are 0.1 M H₂SO₄ and phosphate buffer at pH 2.0 which allow quantitation over a 4 × 10⁻⁶ to 8 × 10⁻⁵ M range using boron-doped diamond and a 1 × 10⁻⁵ to 1 × 10⁻⁴ M range using glassy carbon electrodes, respectively, in supporting electrolyte. All necessary validation parameters were investigated and calculated. These methods were successfully applied for the analysis of fosamprenavir pharmaceutical dosage forms, human serum and urine samples. The standard addition method was used in biological media using boron-doped diamond electrode. No electroactive interferences from the tablet excipients or endogenous substances from biological material were found. The results were statistically compared with those obtained through an established HPLC-UV technique; no significant differences were found between the voltammetric and HPLC methods.     

Selective detection and recovery of gold at tannin-immobilized non-conducting electrode

A tannin-immobilized glassy carbon electrode (TIGC) was prepared via electrochemical oxidation of the naturally occurring polyphenolic mimosa tannin, which generated a non-conducting polymeric film (NCPF) on the electrode surface. The fouling of the electrode surface by the electropolymerized film was evaluated by monitoring the electrode response of ferricyanide ions as a redox marker. The NCPF was permselective to HAuCl₄, and the electrochemical reduction of HAuCl₄ to metallic gold at the TIGC electrode was evaluated by recording the reduction current during cyclic voltammetry measurement. In the mixed electrolyte containing HAuCl₄ along with FeCl₃ and/or CuCl₂, the NCPF remained selective toward the electrochemical reduction of HAuCl₄ into the metallic state. The chemical reduction of HAuCl₄ into metallic gold was also observed when the NCPF was inserted into an acidic gold solution overnight. The adsorption capacity of Au(III) on tannin-immobilized carbon fiber was 29 ± 1.45 mg g⁻¹ at 60 °C. In the presence of excess Cu(II) and Fe(III), tannin-immobilized NCPF proved to be an excellent candidate for the selective detection and recovery of gold through both electrochemical and chemical processes.     

Direct cytochrome c electrochemistry at boron-doped diamond electrodes

Highly boron-doped diamond electrodes are characterized voltammetrically employing Ru(NH₃)₆^3+/2+, Fe(CN)₆^3−/4−, benzoquinone/hydroquinone, and cytochrome c redox systems. The diamond electrodes, which are polished to nanometer finish, are initially `activated' electrochemically and then pretreated by oxidation, reduction, or polishing. All electrodes give reversible cyclic voltammetric responses for the reduction of Ru(NH₃)₆³⁺ in aqueous solution.Redox systems other than Ru(NH₃)₆^3+/2+ show characteristic electrochemical behavior as a function of diamond surface pretreatment. In particular, the horse heart cytochrome c redox system is shown to give reversible voltammetric responses at Al₂O₃ polished boron-doped diamond electrodes. No voltammetric response for cytochrome c is detected at anodically pretreated diamond electrodes. The observations are attributed to preferential interaction of the polished diamond surface with the reactive region of the cytochrome c molecule and low interference due to a lack of protein electrode fouling.     

A study on the determination of chromium as chromate at a carbon paste electrode modified with surfactants

A procedure for the determination of chromium is described based on synergistic pre-concentration of the chromate anion at a carbon paste electrode modified in situ with quarternary ammonium salts such as 1-ethoxycarbonylpentadecyltrimethylammonium bromide (Septonex^®), cetyltrimethylammonium bromide (CTAB) or cetylpyridinium bromide (CPB). The proper electrochemical detection utilises the reduction Cr(VI) → Cr(III) performed in the differential pulse cathodic voltammetric mode. In discussion, considerable attention has been paid to the accumulation mechanism at the carbon paste electrode in the presence of surfactants. Furthermore, after optimising the corresponding experimental conditions (0.1-0.3 M HCl + 0.1 M NaCl as the supporting electrolyte, 2.5-25 μM as the total concentration of modifier, pre-concentration at +0.7 V versus Ag/AgCl and the stripping from +0.7 to −0.4 V), the analytical performance of the method has been evaluated. The signal of interest was reproducible within ±8% and proportional to the concentration in a range of 0.5-50 μM CrO₄²⁻, with a limit of detection (S/N = 3:1) of about 5×10⁻⁸ M CrO₄²⁻ (with accumulation for 300 s). Interference studies were focused mainly on the species capable of forming ion-pairs with the modifier; i.e., TlCl₄⁻, AuCl₄⁻, PdCl₄²⁻, PtCl₆²⁻, VO₄³⁻, MnO₄⁻ and I⁻. Practical applicability of the method was tested on model solutions via the recovery rates (typically 90-110%) or using selected certified reference materials (tea, bush leaves, clover) and two samples of black tea when the respective results were compared to those obtained by the reference determinations with ICP-AES.     

Low-level determination of silicon in steels by anodic stripping voltammetry on a hanging mercury drop electrode

The sensitive differential pulse anodic stripping voltammetry (DPASV) proposed originally by Ishiyama et al. (2001) has been revised and improved to allow the accurate measurement of silicon on a hanging mercury drop electrode (HMDE) instead of a glassy carbon electrode. We assessed the rate of formation of the partially reduced β-silicododecamolybdate and found that metallic mercury promotes the reaction in the presence of a large concentration of Fe³⁺. The scope of the method has been broadened by carrying out the measurements in the presence of a constant amount of Fe³⁺. The limit of detection (LOD) of the method described in the present paper is 100 μg Si g⁻¹ of steel, with a relative precision ranging from 5% to 12%. It can be further enhanced to 700 ng Si g⁻¹ of steel provided the weight of the sample, the dilution factors, the duration of the electrolysis and the ballast of iron are adequately revised. The tolerance to several interfering species has been examined, especially regarding Al³⁺, Cr³⁺ and Cr VI species. The method was validated using four low-alloy ferritic steels certified by the National Institute of Standards and Technology (NIST). Its application to nickel base alloys as well as to less complicated matrixes is straightforward. It has also been successfully applied to the determination of free silicon into silicon carbide nano-powder.     

Utilization of Cr(VI) solutions with steel shavings

New single-stage method was developed for chemical utilization of wastewater containing 0.25 to 400 g L^–1 of chromium in terms of chromium anhydride with the us of sulfuric acid and steel cuttings. The method makes it possible to convert hexavalent chromium into easily used ferrochromium precipitates. It was found that there occur periodic synchronous concentration fluctuations of Cr(VI) and Cr(III) up to, respectively, 400 g L^–1 and 150 mg L^–1 in the course of reduction of hexavalent chromium with the use of steel cuttings in sulfuric acid solutions.     

Electroanalytical investigation and determination of pefloxacin in pharmaceuticals and serum at boron-doped diamond and glassy carbon electrodes

The anodic behavior and determination of pefloxacin on boron-doped diamond and glassy carbon electrodes were investigated using cyclic, linear sweep, differential pulse and square wave voltammetric techniques. In cyclic voltammetry, pefloxacin shows one main irreversible oxidation peak and additional one irreversible ill-defined wave depending on pH values for both electrodes. The results indicate that the process of pefloxacin is irreversible and diffusion controlled on boron-doped diamond electrode and irreversible but adsorption controlled on glassy carbon electrode. The peak current is found to be linear over the range of concentration 2 × 10⁻⁶ to 2 × 10⁻⁴ M in 0.5 M H₂SO₄ at about +1.20 V (versus Ag/AgCl) for differential pulse and square wave voltammetric technique using boron-doped diamond electrode. The repeatability, reproducibility, precision and accuracy of the methods in all media were investigated. Selectivity, precision and accuracy of the developed methods were also checked by recovery studies. The procedures were successfully applied to the determination of the drug in pharmaceutical dosage forms and humans serum samples with good recovery results. No electroactive interferences from the excipients and endogenous substances were found in the pharmaceutical dosage forms and biological samples, respectively.     

Flow injection fluorimetric determination of chromium(VI) in electroplating baths by luminescence quenching of tris(2,2'-bipyridyl) ruthenium(II)

A sensitive and selective luminescence quenching method is developed and used for manual and flow injection analysis (FIA) of chromium(VI) by reaction with [Ru(bpy)₃]²⁺. The emission peak of ruthenium(II) at 595 nm is linearly decreased as a function of Cr(VI) concentration. This permits determination of chromium(VI) ion over the concentration range 0.1-20 μg ml⁻¹ with a detection limit of 33 ng ml⁻¹. The quenching process is due to an electron transfer from the luminescent [Ru(bpy)₃]²⁺ complex ion to Cr(VI) resulting in the formation of the non-luminescent [Ru(bpy)₃]³⁺ complex ion. Selectivity for Cr(VI) over many anions and transition, alkali and alkaline earth metal cations is demonstrated. High concentration levels of sulphate, chloride, borate, acetate, phosphate, nitrate, cyanide, Pb²⁺, Zn²⁺, Hg²⁺, Cu²⁺, Cd²⁺, Ni²⁺ and Mn²⁺ ions are tolerated. The effects of solution pH and [Ru(bpy)₃]²⁺ reagent concentration are examined and the reaction conditions are optimized. Validation of the method according to the quality assurance standards show suitability of the proposed method for use in the quality control assessment of Cr(VI) in complex matrices without prior treatment. The method is successfully applied to determine chromium(VI) in electroplating baths using flow injection analysis. Results with a mean standard deviation of ±0.6% are obtained which compare fairly well with data obtained using atomic absorption spectrometry.     

Dispersion of multi-wall carbon nanotubes in polyhistidine: Characterization and analytical applications

We report for the first time the use of polyhistidine (Polyhis) to efficiently disperse multiwall carbon nanotubes (MWCNTs). The optimum dispersion MWCNT–Polyhis was obtained by sonicating for 30 min 1.0 mg mL⁻¹ MWCNTs in 0.25 mg mL⁻¹ Polyhis solution prepared in 75:25 (v/v) ethanol/0.200 M acetate buffer solution pH 5.00. The dispersion was characterized by scanning electron microscopy, and by cyclic voltammetry and amperometry using ascorbic acid as redox marker. The modification of glassy carbon electrodes with MWCNT–Polyhis produces a drastic decrease in the overvoltage for the oxidation of ascorbic acid (580 mV) at variance with the response observed at glassy carbon electrodes modified just with Polyhis, where the charge transfer is more difficult due to the blocking effect of the polymer. The reproducibility for the sensitivities obtained after 10 successive calibration plots using the same surface was 6.3%. The MWCNT-modified glassy carbon electrode demonstrated to be highly stable since after 45 days storage at room temperature the response was 94.0% of the original. The glassy carbon electrode modified with MWCNT–Polyhis dispersion was successfully used to quantify dopamine or uric acid at nanomolar levels, even in the presence of large excess of ascorbic acid. Determinations of uric acid in human blood serum samples demonstrated a very good correlation with the value reported by Wienner laboratory.     

Simultaneous, sensitive and selective on-line chemiluminescence determination of Cr(III) and Cr(VI) by capillary electrophoresis

A novel in-capillary reduction and capillary electrophoretic (CE)-chemiluminescence (CL) method was developed for the sensitive and selective determination of chromium(III) and chromium(VI). The proposed method was based on the in-capillary reduction of Cr(VI) with acidic H₂O₂ to form Cr(III) using the zone-passing technique and chemiluminescence detection of Cr(III). The sample [Cr³⁺ and CrO₄²⁻], hydrochloric acid, and H₂O₂ (reductant) solution segments were injected for specified periods of time in this order from the anodic end of a capillary, followed by application of an appropriate running voltage between both ends. As both chromium species have opposite charges, Cr³⁺ migrates to the cathode while CrO₄²⁻ ion, moving oppositely to the anode, reacts with acidic H₂O_2, resulted in formation of Cr³⁺. Based on the migration time difference of both Cr³⁺ ions, they were separated by zone electrophoresis. Running buffer was composed of 0.02 mol l⁻¹ HAc-NaAc (pH 4.7) with 1×10⁻³ mol l⁻¹ EDTA. Parameters affecting CE-CL separation and detection, such as reductant concentration, mixing mode of the analytes with CL reagent, CL reaction reagent pH and concentration, stability of luminol-hydrogen peroxide mixed solution were optimized. The limits of detection for chromium(III) and chromium(VI) (3σ) were 6×10⁻¹³ mol l⁻¹ (mass concentration 12 zmol) and 8×10⁻¹² mol l⁻¹ (160 zmol), respectively. This method offered potential advantages of simplicity, sensitivity, selectivity and applicability to the determination of Cr(III) and Cr(VI) in environmental water.     

Reduction of Tetrachloroaurate(III) at Boron-Doped Diamond Electrodes: Gold Deposition Versus Gold Colloid Formation

Tetrachloroaurate(III) dissolved in dilute aqueous aqua regia is electrochemically reduced at boron-doped diamond electrodes to form gold metal. The reduction process is studied by voltammetric, SEM, and XPS techniques. Both the deposition of gold and the anodic stripping process are detected. The ratio of cathodic to anodic charge or stripping efficiency, Q_anodic/Q_cathodic, is shown to depend on the concentration of AuCl and on the pretreatment of the boron-doped diamond electrode surface. Cathodic pretreatment of the boron-doped diamond electrode considerably increases the rate for both deposition and stripping. In the presence of power ultrasound emitted from a glass horn system (24 kHz, 8 Wcm⁻²) the current associated with the reduction of AuCl is considerably enhanced and two components in the mass transport controlled limiting current are identified as (i) the deposition of gold onto the boron-doped diamond and (ii) the formation of colloidal gold.