Detection of aniline at boron-doped diamond electrodes with cathodic stripping voltammetry

Boron-doped diamond (BDD) electrodes were used to investigate the possibility of detecting aniline by linear-sweep cathodic stripping voltammetry. It was found that the dimeric species (p-aminodiphenylamine and benzidine) formed by anodic oxidation of aniline during the accumulation period are involved in electrochemically reversible redox processes and, in acidic media, the shape of the stripping voltammetric response is suitable for aniline detection in the micromolar concentration range. The low background current of conductive diamond is an advantage compared to other electrode materials and allows a detection limit of 1 μM. Weak adsorption properties and the extreme electrochemical stability are additional advantages of BDD and it was found that, even after long-time measurements, the electrode surface can regain its initial activity by an anodic polarization in the potential region of water decomposition.     

Cadmium detection via boron-doped diamond electrodes: surfactant inhibited stripping voltammetry

The deposition of cadmium on boron-doped diamond is investigated with square-wave anodic stripping voltammetry. The system was investigated in quiescent conditions, in the presence of an acoustic field and then in the presence of the neutral surfactant Triton^® X-100. The effect of optimised insonation was to increase the sensitivity from 0.63 (under silent conditions) to 3.78 μA μM⁻¹ and to reduce the limit of detection by an order of magnitude from 10⁻⁸ to 10⁻⁹ M. Measurements with or without insonation were found to deteriorate in the presence of the surfactant. Studies using AFM and chronoamperometry showed that this was due to inhibition of the deposition of the metal. Comparative data obtained for analogous measurements for copper on glassy carbon in the presence of industrial effluent, which also leads to signal deterioration under silent but not insonated conditions, showed that for this case also it was the nucleation of copper rather than the metal dissolution which was adversely affected.     

Fast electrochemical triple-interface processes at boron-doped diamond electrodes

Two important mechanisms for electron transfer processes at boron-doped diamond electrodes involving the oxidation of tetramethylphenylenediamine (TMPD) dissolved in aqueous solution and the oxidation of tetrahexylphenylenediamine (THPD) deposited in the form of microdroplets and immersed into aqueous eletrolyte solution are reported. For TMPD, the first oxidation step in aqueous solution follows the equation: Remarkably slow heterogeneous kinetics at a H-plasma-treated boron-doped diamond electrode are observed, consistent with a process following a pathway more complex than outer-sphere electron transfer. At the same boron-doped diamond electrode surface a deposit of THPD undergoes facile oxidation following the equation: This oxidation and re-reduction of the deposited liquid material occurs at the triple interface organic droplet|diamond|aqueous electrolyte and is therefore an example of a facile high-current-density process at boron-doped diamond electrodes due to good electrical contact between the deposit and the diamond surface. Received: 3 February 2000 / Accepted: 18 February 2000     

Square wave voltammetric determination of nitrofurantoin in pharmaceutical formulations on highly boron-doped diamond electrodes at different boron-doping contents

The influence of the boron-doping levels in boron-doped diamond film electrodes on the electrochemical response of nitrofurantoin (NFT) and the development of an electroanalytical procedure for NFT determination were investigated. The investigations were carried out using the techniques of cyclic voltammetry and square wave voltammetry on diamond film electrodes with different boron-doping levels (i.e., 5000, 10,000 and 20,000 mg L⁻¹). The level of boron-doping in the diamond film electrodes influenced the electrochemical reduction of NFT. The appropriate cyclic voltammetric response of NFT was obtained with Britton-Robinson buffer at pH 4 and for diamond films doped with 10,000 and 20,000 mg L⁻¹ of boron. These two films were selected for the development of the electroanalytical procedure. The use of square wave voltammetry with the optimized parameters demonstrated a good linear relationship between the peak current and the NFT concentration for a wide range of concentration. The lower limit of detection for the electrodes doped with 10,000 and 20,000 mg L⁻¹ of boron were 2.69 × 10⁻⁸ mol L⁻¹ (6.40 μg L⁻¹) and 8.15 × 10⁻⁹ mol L⁻¹ (1.94 μg L⁻¹), respectively, while the lower limits of quantification were 8.96 × 10⁻⁸ mol L⁻¹ (21.33 μg L⁻¹) and 2.72 × 10⁻⁸ mol L⁻¹ (6.47 μg L⁻¹), respectively. The applicability of the proposed procedure was tested using a commercial pharmaceutical formulation of NFT, and the results were compared with the procedure recommended by the British Pharmacopeia. The proposed procedure was sensitive, accurate and precise for analysis of NFT and did not require complex preparations or renovations of the electrode surface. This presents the advantage of eliminating mercury waste and minimizing the adsorptive problems related to the use of other electrodic solid surfaces.     

Crown ethers in stripping voltammetry of palladium

The similarity in the structures (presence of hexatomic rings) of crown ethers and graphite is used for adsorptive modification of the graphite electrode surface. The effect is exploited in stripping voltammetry for the determination of palladium. Anodic currents observed at potentials of 0.6 to 0.65 V (vs. Ag/AgCI electrode) are the source of information about adsorption of the crown ethers. Maximum adsorption of the reagents takes place at potentials close to the potential of zero charge of graphite. Deposition of palladium on the electrode surface is enhanced, the closer the values of the diameters of the crown-ether rings and Pd(II) are.     

Direct electrochemical assay of glucose using boron-doped diamond electrodes

We report linear sweep and square wave voltammetric studies on glucose oxidation at boron-doped diamond (BDD) electrodes in an alkaline medium in efforts to evaluate the techniques for electrochemically assaying glucose. The bare BDD electrode showed good linear responses to glucose oxidation for a concentration range from 0.5 to 10 mM glucose, which well encompasses the physiological range of 3-8 mM. The BDD electrodes did not experience interferences from ascorbic acid or uric acid during glucose detection. This method, when applied to real blood samples, gave results similar to those obtained by a commercial glucose monitor.     

Aliphatic polyamine oxidation response variability and stability at boron-doped diamond thin-film electrodes as studied by flow-injection analysis

Previously it was shown that four different aliphatic polyamines can be quantitatively electrooxidized at boron-doped diamond thin film electrodes without derivatization or the use of pulsed voltammetric waveforms [Anal. Chem. 71 (1999) 1188; Anal. Chem. 69 (1997) 4041]. The flow injection analysis (FIA-EC) investigation (amperometric detection mode) of cadaverine (CAD), putrescine (PUT), spermine (SPM) and spermidine (SPMD), reported previously [Anal. Chem. 71 (1999) 1188], are updated herein with particular emphasis on the electrode response variability and stability. Most of the measurements were made with a film deposited from a 0.50% methane-to-hydrogen (C/H) volumetric ratio. In general, films deposited with C/H ratios near this value tend to possess the requisite physicochemical properties to support anodic oxygen transfer reactions. The electrode performance was evaluated in terms of the linear dynamic range, limit of quantitation, response variability and response stability. A linear dynamic range from 1.0 μM to 1.0 mM and a limit of quantitation of 1.0 μM or 20 pmol injected (S/N≥3) were found for CAD, PUT, and SPMD. For SPM, a linear dynamic range from 0.32 μM to 1.0 mM and a limit of quantitation of 0.32 μM or 6.4 pmol were observed. The response variability, as low as 2–4%, was observed which is vastly improved over previous results. The improvement was achieved by introducing a 3–6 min delay period between injections. The long-term response stability was good with no evidence for any progressive response attenuation or complete fouling by the reaction product, even though a solid deposit was observed to accumulate on the electrode surface with extended use. The deposit appears to partially reduce the active electrochemical area for polyamine oxidation and to decrease the overpotential for water discharge. Preliminary chromatographic results demonstrated the possibility of separating and detecting the polyamines by a simple reverse-phase scheme at constant applied potential.     

Recent electroanalytical applications of boron-doped diamond electrodes

This review overviews recent reports on the electroanalytical applications of boron-doped diamond (BDD) electrodes. Because BDD electrodes have excellent features for electroanalysis, such as wide potential window, low background current, electrochemical stability, and fouling resistance, they can be useful for sensitive and stable detection of various substances, including drugs, bio-related substances, metal ions, and organic pollutants. Many articles have reported high-sensitivity detection of real samples, demonstrating that this electrode material is practically applicable. Surface modification of the BDD electrodes using metal nanoparticles, nanocarbons, and polymers can increase the sensitivity of the electrochemical detection. Furthermore, research on the electroanalytical device equipped with BDD electrodes will be expanded by combining peripheral technologies related to the device fabrication.     

Electroanalysis of myoglobin and hemoglobin with a boron-doped diamond electrode

The electrochemical behavior of myoglobin (Mb) and hemoglobin (Hb) was investigated with a boron-doped diamond (BDD) electrode by cyclic voltammetry. In acetate buffer solutions, the oxygen reduction at the BDD electrode showed a very high overpotential while the reduction of Mb or Hb was observed in the more positive potential region. Owing to the electrocatalytic reaction of O₂ and the participation of H⁺ following the electrochemical reduction of ferric proteins, the voltammetric responses for Mb and Hb on the BDD electrode in the negative going scans became remarkable in acidic buffer solutions in air. The peak current was linearly proportional to the concentration of Mb in the range 1×10⁻⁶–2×10⁻⁵ M or the concentration of Hb from 1×10⁻⁶ to 1×10⁻⁵ M.     

Application of boron-doped diamond electrodes for electrochemical oxidation of real wastewaters

Recently, the synthesis of boron-doped diamond electrodes on different substrates and shapes have reached a promising development stage. Now, these electrodes can also be effectively used to destroy toxic or biorefractory organics in real effluents, such as municipal wastewaters effluents, hospital wastewaters, groundwater, petrochemical effluent, wastewaters from agri–food activities, and so on. The results of this mini-review show that BDD is effectively even for such real effluents, allowing the removal of pollutants under several different conditions. Nevertheless, further efforts are necessary to reach a wider market; in particular, the next stages must face the optimization of cell design and the integration of the electrochemical system with other water treatment and renewable energy sources.     

The application of boron-doped diamond electrodes in amperometric biosensors

Boron-doped diamond (BDD) electrodes outperform conventional electrodes in terms of high stability, chemical inertness, wide potential window and low background current. Combining the superior properties of BDD electrodes with the merits of biosensors, such as specificity, sensitivity, and fast response, amperometric biosensors based on BDD electrodes have attracted the interests of many researchers. In this review, the latest advances of BDD electrodes with different surfaces including hydrogen-terminated, oxygen-terminated, metal nanoparticles-modified, amine-terminated, and carboxyl-terminated thin films, and microelectrodes, for the construction of various biosensors or the direct detection of biomolecules were demonstrated. The future trends of BDD electrodes in biosensing were also discussed.     

Influencing factors of venlafaxine degradation at boron-doped diamond anode

Degradation of the antidepressant venlafaxine by an effective electrocatalytic process, boron-doped diamond (BDD) electrode, was study. The BDD electrode was selected as the anode, and the degradation efficiency of venlafaxine under different influencing factors was systematically investigated. The preliminary grasp of the degradation law of venlafaxine by anodic electro-degradation using BDD electrode was obtained. The experimental results showed that the electrochemical oxidation technology using BDD anode can effectively degrade venlafaxine and remove total organic carbon (TOC) from the solution, complete venlafaxine degradation and TOC elimination could be achieved within 30 and 120 min of BDD oxidation process, respectively, and it has good stability and reusability. Increasing the electrolyte concentration (≤0.1 mol/L) and current density (≤100 mA/cm²) within a certain range could accelerate the degradation of venlafaxine. HCO₃^– and PO₄^3? could inhibit the degradation efficiency of venlafaxine through of competing for free radicals. It is interesting that the presence of Cl^? significantly promoted the degradation efficiency of venlafaxine. The results of this study suggest that the Electro-degradation treatment may provide a promising way to treat venlafaxine contaminated water.     

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.     

Voltammetric determination of aminobiphenyls at a boron-doped nanocrystalline diamond film electrode

Voltammetric behavior of 2-aminobiphenyl, 3-aminobiphenyl, and 4-aminobiphenyl at a boron-doped nanocrystalline diamond film electrode was investigated using cyclic voltammetry and differential pulse voltammetry. Optimum conditions have been found for the determination of those genotoxic substances by differential pulse voltammetry at the above given electrode in the concentration range of 2 × 10⁻⁷ to 1 × 10⁻⁵ mol/L.     

Simultaneous voltammetric determination of paracetamol and caffeine in pharmaceutical formulations using a boron-doped diamond electrode

A simple and highly selective electrochemical method was developed for the single or simultaneous determination of paracetamol (N-acetyl-p-aminophenol, acetaminophen) and caffeine (3,7-dihydro-1,3,7-trimethyl-1H-purine-2,6-dione) in aqueous media (acetate buffer, pH 4.5) on a boron-doped diamond (BDD) electrode using square wave voltammetry (SWV) or differential pulse voltammetry (DPV). Using DPV with the cathodically pre-treated BDD electrode, a separation of about 550 mV between the peak oxidation potentials of paracetamol and caffeine present in binary mixtures was obtained. The calibration curves for the simultaneous determination of paracetamol and caffeine showed an excellent linear response, ranging from 5.0 × 10⁻⁷ mol L⁻¹ to 8.3 × 10⁻⁵ mol L⁻¹ for both compounds. The detection limits for the simultaneous determination of paracetamol and caffeine were 4.9 × 10⁻⁷ mol L⁻¹ and 3.5 × 10⁻⁸ mol L⁻¹, respectively. The proposed method was successfully applied in the simultaneous determination of paracetamol and caffeine in several pharmaceutical formulations (tablets), with results similar to those obtained using a high-performance liquid chromatography method (at 95% confidence level).     

Electrochemical reduction of CO2 and degradation of KHP on boron-doped diamond electrodes in a simultaneous and enhanced process

A BDD-BDD system was developed in the simultaneous conversion of CO₂ and wastewater purification in one electrochemical cell.     

Effect of the mediator in feedback mode-based SECM interrogation of indium tin-oxide and boron-doped diamond electrodes

Indium tin-oxide (ITO) and polycrystalline boron-doped diamond (BDD) have been examined in detail using the scanning electrochemical microscopy technique in feedback mode. For the interrogation of electrodes made from these materials, the choice of mediator has been varied. Using ferrocene methanol (FcMeOH), and approach curve experiments have been performed, and for purposes of comparison, calculations of the apparent heterogeneous electron transfer rates (k _app) have been made using these data. In general, it would appear that values of k _app are affected mainly by the position of the mediator reversible potential relative to the relevant semiconductor band edge (associated with majority carriers). For both the ITO (n type) and BDD (p type) electrodes, charge transfer is impeded and values are very low when using FcMeOH and as mediators, and the use of results in the largest value of k _app. With ITO, the surface is chemically homogeneous and no variation is observed for any given mediator. Data is also presented where the potential of the ITO electrode is fixed using a ratio of the mediators and In stark contrast, the BDD electrode is quite the opposite and a range of k _app values are observed for all mediators depending on the position on the surface. Both electrode surfaces are very flat and very smooth, and hence, for BDD, variations in feedback current imply a variation in the electrochemical activity. A comparison of the feedback current where the substrate is biased and unbiased shows a surprising degree of proportionality.Dedicated to Alan, a good friend and colleague on his 60th birthday.     

Electroanalytical applications of boron-doped diamond microelectrode arrays

The electrochemical characteristics of a novel all diamond fabricated boron-doped diamond microelectrode array (BDD-MEA) are critically appraised. The voltammetric response of simple electron transfer processes has been investigated and found to generate sigmoidal voltammetric curves. Furthermore, the device has been utilized for various analytical applications including, the direct detection of 4-nitrophenol over the concentration range 1.8-9.2 μM, manganese over the range 0.1-4.8 μM and the indirect determination of sulfide producing a limit of detection of 23 μM.     

Structural and electrochemical heterogeneities of boron-doped diamond surfaces

This brief review is focussed on the recent progress in studies of the heterogeneous electrochemical behaviour of various boron-doped materials extending from zero-dimensional particles through polycrystalline or nanostructured three-dimensional surfaces. A boron-doped diamond reveals large heterogeneities induced by numerous factors, inter alia multi-faceted crystallinity, inhomogeneous boron concentration, sp²/sp³-carbon ratio, surface terminations and grain size distribution. We also present single nanodiamond particles and a nanostructured diamond, which are fabricated by either a top-down or a bottom-up procedure. Nanoarchitectured surfaces allow high areas and large aspect ratios to be achieved, exhibiting highly heterogeneous charge-transfer performance for catalytic, sensing and energy applications. We have anticipated multi-factor-originated heterogeneities of various boron-doped diamond surfaces displaying the essential fabrication and diagnostic methodologies and critically reviewing their benefits and drawbacks.