Comparison of Boron‐Doped Diamond and Glassy Carbon Electrodes for Determination of Procaine Hydrochloride

The electrochemical oxidation of procaine hydrochloride (PC?HCL, 2‐diethylaminoethyl 4‐aminobenzoate hydrochloride) was investigated at as‐deposited boron‐doped diamond (ad‐BDD) electrode, anodically oxidized BDD (ao‐BDD) electrode and glassy carbon (GC) electrode using cyclic voltammetry (CV). Well‐defined cyclic voltammograms were obtained for PC?HCL oxidation with high signal‐to‐background (S/B) ratio, low tendency for adsorption, good reproducibility and long‐term stability at ad‐BDD electrode, demonstrating its superior electrochemical behavior and significant advantages in contrast to ao‐BDD and GC electrode. At 100 μM PC?HCL, the voltammetric S/B ratio was nearly one order of magnitude higher at an ad‐BDD electrode than that at a GC electrode. In a separate set of experiments for oxidation of 100 μM PC?HCL, 96%, 92% and 84% of the initial oxidation peak current was retained at the ad‐BDD, ao‐BDD and GC electrode, respectively, by stirring the solution after the tenth cycle. The current response was linearly proportional to the square root of the scan rate within the range 10–1000 mV s^?1 in 10 μM PC?HCL solutions, indicating that the oxidation process was diffusion‐controlled with negligible adsorption at an ad‐BDD surface. The good linearity was observed for a concentration range from 5 to 200 μM with a linear equation of y=0.03517x+0.65346 (r=0.999), and the detection limit was 0.5 μM for oxidation of PC?HCL at the ad‐BDD electrode. The ad‐BDD electrode could maintain 100% of its original activity after intermittent use for 3 months.     

Voltammetric Assay of Naproxen in Pharmaceutical Formulations Using Boron‐Doped Diamond Electrode

The electrooxidation of naproxen was studied, for the first time, using boron‐doped diamond (BDD) electrode by cyclic and differential pulse voltammetry (CV and DPV) in nonaqueous solvent supporting electrolyte system. The results were also compared with glassy carbon electrode (GC) under the same conditions. Naproxen undergoes one electron transfer resulting in the formation of cation radical for the first electrooxidation step, which follows other chemical and electrochemical steps such as deprotonation, removal of another electron and the attack of nucleophile (ECEC mechanism). BDD electrode provided higher signal to background ratio, well resolved and highly reproducible cyclic voltammograms than the GC electrode. With a scan rate of 50 mV s^?1 and pulse height of 50 ms, respectively, the DPV technique was able to determine the naproxen concentrations in the range of 0.5 to 50 μM with a detection limit of 30 nM. The influence of interference compounds namely 2‐acetyl‐6‐methoxy naphthalene (AMN) on naproxen oxidation can also be followed successfully. Moreover, the percentage of AMN present in the standard chemical form of a mixture containing naproxen can be found accurately. Rapidity, precise and good selectivity were also found for the determination of naproxen in pharmaceutical formulations.     

A flow injection method for the analysis of tetracycline antibiotics in pharmaceutical formulations using electrochemical detection at anodized boron-doped diamond thin film electrode

A method using flow injection (FI) with amperometric detection at anodized boron-doped diamond (BDD) thin films has been developed and applied for the determination of tetracycline antibiotics (tetracycline, chlortetracycline, oxytetracycline and doxycycline). The electrochemical oxidation of the tetracycline antibiotics was studied at various carbon electrodes including glassy carbon (GC), as-deposited BDD and anodized BDD electrodes using cyclic voltammetry. The anodized BDD electrode exhibited well-defined irreversible cyclic voltammograms for the oxidation of tetracycline antibiotics with the highest current signals compared to the as-deposited BDD and glassy carbon electrodes. Low detection limit of 10 nM (signal-to-noise RATIO = 3) was achieved for each drug when using flow injection analysis with amperometric detection at anodized BDD electrodes. Linear calibrations were obtained from 0.1 to 50 mM for tetracycline and 0.5–50 mM for chlortetracycline, oxytetracycline and doxycycline. The proposed method has been successfully applied to determine the tetracycline antibiotics in some drug formulations. The results obtained in percent found (99.50–103.01%) were comparable to dose labeled.     

Rapid Nanomolar Detection of Guaiacol from its Precursors Using a Core-shell Reversed-phase Column Coupled with a Boron-doped Diamond Electrode

The electrooxidation mechanisms of guaiacol (2-methoxyphenol), a food and beverage spoilage metabolite, and its precursors; vanillic acid (VA), vanillin, and ferulic acid (FA) were investigated by cyclic voltammetry (CV) with a boron-doped diamond (BDD) electrode. Reversed-phase liquid chromatography (RPLC) together with a BDD electrode poised at +1.6 V vs. Pd/H₂, was optimized for their sensitive detection. The separation was achieved in 60 s with a core-shell column (HALO C₁₈). The detection limits of these analytes ranged from 10–30 nM. The method was applicable for the analysis of guaiacol and its precursors from a popular commercial drink.     

Electrochemical analysis of -penicillamine using a boron-doped diamond thin film electrode applied to flow injection system

The electroanalysis of -penicillamine in 0.1 phosphate buffer (pH 7) was studied at a boron-doped diamond thin film (BDD) electrode using cyclic voltammetry as a function of concentration of analyte and pH of analyte solution. Comparison experiments were performing using a glassy carbon (GC) electrode. The BDD electrode exhibited a well-resolved and irreversible oxidation voltammogram, but the GC electrode provided only an ill-defined response. The BDD electrode provided a linear dynamic range from 0.5 to 10 mM and a detection limit of 25 μM (S/B≥3) in voltammetric measurement. It was also found that the peak potentials were decreased when the pH of the analyte solution was increased. In addition, penicillamine has been studied by hydrodynamic voltammetry and flow injection analysis with amperometric detection using the BDD electrode. The flow injection analysis results at the diamond electrode indicated a linear dynamic range from 0.5 to 50 μM and a detection limit of 10 nM (S/N≈4). The proposed method was applied to determine -penicillamine in dosage form (capsules), the results obtained in the recovery study (255±2.50 mg per tablet) were comparable to those labeled (250 mg per tablet).     

Electrochemical detection of ascorbic acid and serotonin at a boron-doped diamond electrode modified with poly(N,N-dimethylaniline)

The electrochemical oxidation of ascorbic acid (AA) and serotonin (5-HT) at a boron-doped diamond (BDD) electrode modified with poly(N,N-dimethylaniline) (PDMA) has been studied. The oxidation potentials of 5-HT and AA overlapped after mixing of the two chemicals, due to interference of AA at the bare BDD electrode. However, after modifying the BDD electrode with a cationic polymer (PDMA), the oxidation peaks of 5-HT and AA were separated. PDMA-coated BDD electrodes can be used for simultaneous detection of these species.     

Electrochemical analysis of d-penicillamine using a boron-doped diamond thin film electrode applied to flow injection system

The electroanalysis of d-penicillamine in 0.1 phosphate buffer (pH 7) was studied at a boron-doped diamond thin film (BDD) electrode using cyclic voltammetry as a function of concentration of analyte and pH of analyte solution. Comparison experiments were performing using a glassy carbon (GC) electrode. The BDD electrode exhibited a well-resolved and irreversible oxidation voltammogram, but the GC electrode provided only an ill-defined response. The BDD electrode provided a linear dynamic range from 0.5 to 10 mM and a detection limit of 25 muM (S/B>/=3) in voltammetric measurement. It was also found that the peak potentials were decreased when the pH of the analyte solution was increased. In addition, penicillamine has been studied by hydrodynamic voltammetry and flow injection analysis with amperometric detection using the BDD electrode. The flow injection analysis results at the diamond electrode indicated a linear dynamic range from 0.5 to 50 muM and a detection limit of 10 nM (S/N approximately 4). The proposed method was applied to determine d-penicillamine in dosage form (capsules), the results obtained in the recovery study (255+/-2.50 mg per tablet) were comparable to those labeled (250 mg per tablet).     

The Determination of Methanol Using an Electrolytically Fabricated Nickel Microparticle Modified Boron Doped Diamond Electrode

A nickel modified boron doped diamond (Ni‐BDD) electrode and nickel foil electrode were used in the determination of methanol in alkaline solutions. The Ni‐BDD electrode was electrodeposited from a 1 mM Ni(NO₃)₂ solution (pH 5), followed by repeat cycling in KOH. Subsequent analysis utilised the Ni(OH)₂/NiOOH redox couple to electrocatalyse the oxidation of methanol. Methanol was determined to limits of 0.3 mM with a sensitivity of 110 nA/mM at the Ni‐BDD electrode. The foil electrode was less sensitive achieving a limit of 1.6 mM and sensitivity of 27 nA/mM. SEM analysis of the electrodes found the Ni‐BDD to be modified by a quasi‐random microparticle array.     

Localisation and quantification of benzalkonium chloride in eye tissue by TOF-SIMS imaging and liquid chromatography mass spectrometry

Benzalkonium (BAK) chloride is the most commonly used preservative in eye drops. It is generally composed of benzyldimethyldodecylammonium C₁₂ and benzyldimethyltetradecylammonium C₁₄ and is supposed to increase penetration of active compounds. However, numerous studies have reported its toxic effect to ocular surface especially in long-term treatments like against glaucoma, a sight-threatening disease. Albino rabbits were treated with a hyperosmolar solution and a high concentration of BAK solution for 1 month. Enucleated eyes were cryo-sectioned and analysed by mass spectrometry. Mass spectrometry imaging using time-of-flight secondary ion mass spectrometry (TOF-SIMS) has been used to characterize the spatial distribution and to determine the relative quantity of BAK at the surface of rabbit eye sections. Liquid chromatography coupled with mass spectrometry (LC-MS) using a hybrid linear ion trap-Orbitrap® mass spectrometer was used to obtain relative quantification of BAK at the sample surface. TOF-SIMS images of BAK ions indicated a distribution at the ocular surface and in deeper structures. Didecyldimethylammonium (DDMAC), which is used in hospitals as a substitute for BAK, was also detected and showed an accumulation around the eyes. After extraction with acetonitrile and chromatographic separation using a Gemini C18 column and an original elution gradient, the relative quantities of BAK and DDMAC present in the whole eye section surface were determined. This LC-MS method was validated in terms of limits of quantification, linearity, repeatability and reproducibility and its feasibility was evaluated in surgically obtained human samples. Specimens of iris, lens capsule or trabecular meshwork were found with significant levels of BAK and DDMAC, thus confirming the penetration of BAK in deep ocular structures, with potential deleterious effects induced by this cytotoxic compound. The analytical method developed here could therefore be of primary interest in the field of pharmaco-toxicology in order to localise, identify and quantify drugs or xenobiotic compounds present at biological sample surfaces.

Use of a Boron-Doped Diamond Electrode for Amperometric Assay of Bromide and Iodide Ions

The electrochemical assay of bromide and iodide ions at boron-doped diamond (BDD) electrode was investigated by cyclic voltammetry (CV) and chronoamperometry (CA). Comparison experiments were carried out using a glassy carbon (GC) electrode. The BDD electrode exhibited well-resolved and irreversible reduction voltammograms, while the GC electrode provided only an ill-defined response. Cyclic voltammetric signals at BDD electrode for 10 mM Br⁻ and I⁻ were observed at 561 and 125 mV vs. SCE; the values shifted negatively for 228.7 and 187.5 mV, respectively, compared to those at GC electrode. It was also found that the peak current of Br⁻ and I⁻ was in direct proportion to the scan rate, which is indicative of a surface confined reduction process. Sensitive amperometric responses for Br⁻ and I⁻ were obtained covering the linear ranges 0.666 μM–1 mM and 13.3 nM–1 mM, respectively, and their detection limits were 0.53 μM and 1.67 nM, respectively, under the optimum pH and applied potential. The amperometric response was very reproducible and stable with satisfactory recovery results. __________ From Zhurnal Analiticheskoi Khimii, Vol. 60, No. 11, 2005, pp. 1193–1199. Original English Text Copyright ? 2005 by Jing Wu, Xiaoli Li, Cunxi Lei, Xumei Wu, Guoli Shen, and Rugin Yu. This article was submitted by the authors in English.     

Simultaneous Differential Pulse Voltammetric Determination of Sulfamethoxazole and Trimethoprim on a Boron‐Doped Diamond Electrode

The performance of hydrogen‐ (HT) and oxygen‐terminated (OT) boron‐doped diamond (BDD) electrodes (electrochemically pretreated) on the simultaneous differential pulse voltammetric determination of sulfamethoxazole and trimethoprim in pharmaceutical products is presented. Under the optimum analytical experimental conditions, the HT‐BDD electrode presented two well‐defined oxidation peaks at 920 and 1100 mV vs. Ag/AgCl for sulfamethoxazole and trimethoprim, respectively. On the other hand, when the OT‐BDD electrode was used, the sulfamethoxazole oxidation current peak was decreased twenty fold. The calculated LOD values for sulfamethoxazole and trimethoprim using the HT‐BDD electrode were 3.65 μg L^?1 and 3.92 μg L^?1, respectively. The results obtained in the simultaneous determination of sulfamethoxazole and trimethoprim in three different commercial formulations were similar to those obtained using a standard HPLC method at 95% confidence level.     

Electrochemical Detection of Catechol on Boron‐doped Diamond Electrode Modified with Au/TiO2 Nanorod Composite

Au/TiO₂ nanorod composites with different ratios of [TiO₂]:[Au] have been prepared by chemically reducing AuCl₄^‐ on the positively charged TiO₂ nanorods surface and used to modify boron‐doped diamond (BDD) electrodes. The electrochemical behaviors of catechol on the bare and different Au/TiO₂ nanorod composites‐modified BDD electrodes are studied. The cyclic voltammetric results indicate that these different Au/TiO₂ nanorod composites‐modified BDD electrodes can enhance the electrocatalytic activity toward catechol detection, as compared with the bare BDD electrode. Among these different conditions, the Au/TiO₂‐BDD3 electrode (the ratio of [TiO₂]:[Au] is 27:1) is the most choice for catechol detection. The electrochemical response dependences of the Au/TiO₂‐BDD3 electrode on pH of solution and the applied potential are studied. The detection limit of catechol is found to be about 1.4 × 10^‐6 M in a linear range from 5 × 10^‐6 M to 200 × 10^‐6 M on the Au/TiO₂‐BDD3 electrode.     

Photocatalytically-assisted electrochemical degradation of <Emphasis Type="Italic">p</Emphasis>-aminophenol in aqueous solutions using zeolite-supported TiO<Subscript>2</Subscript> catalyst

This paper reports the results of an investigation into enhancement of the electrochemical oxidation of p-aminophenol (4-AP) in an aqueous solution with a boron-doped diamond (BDD) electrode, assisted by photocatalysis using a zeolite-supported TiO₂ (Z-TiO₂) catalyst. The BDD electrode was characterised in 0.1 M Na₂SO₄-supporting electrolyte and the presence of 4-AP by open-circuit potential behaviour (OCP) and cyclic voltammetry (CV). The electrode behaviour was investigated in the dark and following UV irradiation and in the absence/presence of the Z-TiO₂ catalyst. The electro-oxidation process was carried out using chronoamperometry (CA) and multiple-pulsed amperometry (MPA) at the selected potential under potentiostatic conditions. The electrochemical degradation process of 4-AP on the BDD electrode was improved by the application of a pulsed potential, which allowed both in-situ electrochemical cleaning of the electrode and indirect oxidation of 4-AP by oxygen evolution. The application of photocatalysis using Z-TiO₂ in the 4-AP electrochemical degradation exhibited an enhanced effect when the anodic potential was set at +1.25 V vs. Ag/AgCl in the water stability region, close to the oxygen evolution potential.     

Electrochemical oxidation of phenol on boron-doped diamond electrode

The process of phenol oxidation on a boron-doped diamond electrode (BDD) is studied in acidic electrolytes under different conditions of generation of active oxygen forms (AOFs). The scheme of phenol oxidation known from the literature for other electrode materials is confirmed. Phenol is oxidized through a number of intermediates (benzoquinone, carboxylic acids) to carbon dioxide and water. Comparative analysis of phenol oxidation rate constants is performed as dependent on the electrolysis conditions: direct anodic oxidation, with oxygen bubbling, and addition of H₂O₂. A scheme is confirmed according to which active radicals (OH^·, HO₂^·, HO₂⁻) are formed on a BDD anode that can oxidize the substrate which leads to formation of organic radicals interacting with each other and forming condensation products. Processes with participation of free radicals (chain-radical mechanism) play an important role in electrochemical oxidation on BDD. Intermediates and polymeric substances (polyphenols, quinone structures, and resins) are formed. An excess of the oxidant (H₂O₂) promotes a more effective oxidation of organic radicals and accordingly inhibition of the condensation process.     

The Electro‐Oxidation of Formaldehyde at a Boron‐Doped Diamond Electrode

Abstract

The characteristics of the boron‐doped diamond (BDD) electrode in this work were studied by atomic force microscope (AFM), scanning electron microscopy, and Raman spectroscopy. The electro‐oxidation of formaldehyde at the BDD electrode in 0.5 M K₂SO₄ with different pH was studied by cyclic voltammetry and amperometry. There is no significant oxidation peak of formaldehyde in acidic solution because the oxidation of formaldehyde is at the potential range of water discharge. However, in neutral solution, there is a well‐defined oxidation peak at about +2.2 V vs. Ag/AgCl. The relation between the response current and formaldehyde concentration is linear behavior at the concentration range from 50 to 600 µM. Besides, in neutral solution, the oxidation of formaldehyde is dominated by indirect oxidation at lower formaldehyde concentration, and it is dominated by direct oxidation at higher concentration. Finally, in alkaline solution, the oxidation of formaldehyde is dominated by indirect oxidation caused by a powerful oxidant and is related to the ratio of the amounts of formaldehyde and OH molecules at the BDD electrode surface.     

Investigation of electro-oxidation of methanol and benzyl alcohol at boron-doped diamond electrode: evidence for the mechanism for fouling film formation

Boron-doped diamond (BDD) and glassy carbon (GC) electrodes are compared for electrochemical oxidation of methanol and benzyl alcohol. Cyclic voltammograms reveal that BDD electrode produces good oxidation signals for both methanol and benzyl alcohol, while GC produces no significant oxidation signal for either methanol or benzyl alcohol. Amperometric measurement of oxidation of methanol and benzyl alcohol on BDD shows development of a fouling film for benzyl alcohol but not for methanol. Prolonged (24 h) polarization of the BDD electrode at +2.0 V in benzyl alcohol generated enough fouling film for investigation by AFM, SEM, Raman, and FTIR techniques. AFM and SEM microscopy images confirm a fouling film confined to the low-lying regions of the polycrystallite BDD surface, indicating that the active sites of benzyl alcohol oxidation are located within these low-lying regions. The fouling material generated in the process of benzyl alcohol oxidation was identified from Raman and FTIR spectroscopy as polyester. Experiments confirm the fouling film can be removed and the electrode surface reactivated by brief polarization at +3.0 V. Amperometric results of concentration dependence confirm the BDD electrode is well suited for quantitative analysis applications of methanol and benzyl alcohol, with recognizable oxidation currents at micromolar concentration levels.     

Electrochemical and ESR study of the mechanism of oxidation of phenazine-di-N-oxide in the presence of cyclohexanol on glassy carbon and single-walled carbon nanotube electrodes

The mechanism of oxidation of phenazine-di-N-oxide in the presence of cyclohexanol was studied by cyclic voltammetry on glassy carbon (GC) and single-walled carbon nanotube (SWCNT) electrodes in 0.1 M LiClO₄ solutions in acetonitrile. The effect of cyclohexanol on the shape of the cyclic voltammograms of phenazine-di-N-oxide and the intensity of the ESR signal of its radical cation was investigated. It was shown by ESR that the products of the one-electron oxidation and reduction of phenazine-di-N-oxide were radical cations and anions. The catalytic currents were recorded during the oxidation of phenazine-di-N-oxide on the SWCNT and GC electrodes in the presence of cyclohexanol. The results were explained in terms of the E₁C₁E₂C₂ mechanism of the two-stage electrode process characterized by the catalytic current recorded at the second electrode stage. The overall two-electron catalytic oxidation of cyclohexanol in the complex with the phenazine-di-N-oxide radical cation was assumed to occur. It was shown that SWCNT electrodes can be used in the electrocatalytic oxidation of organic compounds in the presence of the electrochemically generated phenazine-di-N-oxide radical cation.     

Fabrication and characterization of boron doped diamond microelectrode arrays of varied geometry

Boron doped diamond (BDD) is a well-known electrode material that exhibits an excellent electrochemical potential window with very low background current. With this, microelectrodes and microelectrode arrays (MEAs) have been found to even further lower background currents without compromising sensitivity. As such, BDD MEAs are excellent electrode materials for a variety of electroanalytical applications, capable of multi-mode detection. We fabricated BDD MEAs adapting traditional semiconductor microfabrication processes; the resulting MEAs were patterned in different geometries to find an optimum electrochemical response, depending on the application. This is demonstrated using 4 different MEA geometries of different size and spacing using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), where the charge transfer resistance (R_ct) increases as the electrodes are farther spaced from one another. Excellent sigmoidal voltammogram shape in CV was obtained for each BDD MEA geometry. BDD MEAs spaced farther from one another were found to give better resolution from the background in fast scan cyclic voltammetric measurements of dopamine due to the decrease in the double layer capacitance (C_dl) as verified with EIS. This work furthers the understanding of BDD MEAs and their pertinence to sensitive electroanalytical techniques.     

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.     

Simultaneous detection of purine and pyrimidine at highly boron-doped diamond electrodes by using liquid chromatography

Highly boron-doped diamond (BDD) electrode, have been examined for simultaneous detection of purine and pyrimidine bases in mild acidic media by using HPLC with amperometric detection. Cyclic voltammetry at as-deposited (AD) and anodically oxidized (AO) BDD were used to study the electrochemistry and to optimize the condition for HPLC applications. At AO BDD electrode, due to its higher overpotential of oxygen evolution reaction, well-defined anodic peaks were observed for the oxidation of purine and pyrimidine bases in acid medium, whereas at AD BDD the oxidation peak of thymine was overlapped with the anodic current of oxygen evolution. The chromatograms of adenine, guanine, cytosine, thymine and 5-methylcytosine mixture were well resolved by using a silica-based column and a solution of 5% acetonitrile in 100 mM ammonium acetate buffer (pH 4.25) as the mobile phase. The detection was carried out at AO BDD electrode at an applied potential of 1.6 V versus Ag/AgCl. Linear calibration curves were obtained within the concentration range from 0.1 to 10 μM with the limits of detection (S/N = 3) ranging from 26.3 to 162.1 nM, resulting in an order of magnitude higher sensitivities than those at conventional electrodes. HPLC analysis with diamond amperometric detector was successfully applied for determination of 5-methylcytosine in real DNA samples with high reproducibility. No deactivation of the electrode was found during cyclic voltammetric and HPLC measurements, indicating the high stability for analysis of biological samples.