Anodic Oxidation Behaviors of Formaldehyde at Boron‐Doped Diamond Electrodes

The electrochemical behaviors of formaldehyde (FA) at boron‐doped diamond (BDD) electrodes are investigated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and linear scanning voltammetry (LSV) techniques. The CV results show that the oxidation reaction of FA is influenced by the hydroxyl concentration in the solution, and the peak current response with the FA concentration is linear at the range from 10 to 100 mM. The differential capacitance from EIS results indicate that the FA molecules adsorb at the BDD electrode surface at low potential (from 1.0 to 1.4 V). The kinetic studies have been examined with the various concentrations of FA, pH, and temperature. The activation energy of FA oxidation is also calculated. The results of kinetic study indicate that the adsorption of FA molecules at the BDD electrode is the rate‐determining step at low potential (from 1.0 to 1.40 V).     

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.     

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.     

Electrochemical Behavior and Electroanalytical Determination of Indole‐3‐Acetic Acid Phytohormone on a Boron‐Doped Diamond Electrode

In this work, a boron‐doped diamond (BDD) electrode was used for the electroanalytical determination of indole‐3‐acetic acid (IAA) phytohormone by square‐wave voltammetry. IAA yielded a well‐defined voltammetric response at +0.93 V (vs. Ag/AgCl) in Britton–Robinson buffer, pH 2.0. The process could be used to determine IAA in the concentration range of 5.0 to 50.0 µM (n=8, r=0.997), with a detection limit of 1.22 µM. The relative standard deviation of ten measurements was 2.09 % for 20.0 µM IAA. As an example, the practical applicability of BDD electrode was tested with the measurement of IAA in some plant seeds.     

Electroanalytical Determination of N‐Nitrosamines in Aqueous Solution Using a Boron‐Doped Diamond Electrode

The electrochemical methods cyclic and square‐wave voltammetry were applied to develop an electroanalytical procedure for the determination of N‐nitrosamines (N‐nitrosopyrrolidine, N‐nitrosopiperidine and N‐nitrosodiethylamine) in aqueous solutions. Cyclic voltammetry was used to evaluate the electrochemical behaviors of N‐nitrosamines on boron‐doped diamond electrodes. It was observed an irreversible electrooxidation peak located in approximately 1.8 V (vs. Ag/AgCl) for both N‐nitrosamines. The optimal electrochemical response was obtained using the following square‐wave voltammetry parameters: f=250 Hz, E_sw=50 mV and E_s=2 mV using a Britton–Robinson buffer solution as electrolyte (pH 2). The detection and quantification limits determined for total N‐nitrosamines were 6.0×10^?8 and 2.0×10^?7 mol L^?1, respectively.     

Simultaneous Differential Pulse Voltammetric Determination of Ascorbic Acid and Caffeine in Pharmaceutical Formulations Using a Boron‐Doped Diamond Electrode

A cathodically pretreated boron‐doped diamond electrode was used for the simultaneous anodic determination of ascorbic acid (AA) and caffeine (CAF) by differential pulse voltammetry. Linear calibration curves (r=0.999) were obtained from 1.9×10^?5 to 2.1×10^?4 mol L^?1 for AA and from 9.7×10^?6 to 1.1×10^?4 mol L^?1 for CAF, with detection limits of 19 μmol L^?1 and 7.0 μmol L^?1, respectively. This method was successfully applied for the determination of AA and CAF in pharmaceutical formulations, with results equal to those obtained using a HPLC reference method.     

Sensitive Electrochemical Detection of Oxalate at a Positively Charged Boron‐Doped Diamond Surface

Allyltriethylammonium bromide (ATAB) was covalently attached to the surface of hydrogen‐terminated boron‐doped diamond (BDD) thin films using a photochemical method to fabricate positively charged electrode surfaces. The anodic current for oxalate oxidation both in cyclic voltammetry and in flow‐injection analysis with amperometry was found to be up to two times larger at ATAB‐modified BDD (ATAB‐BDD) than at an unmodified BDD electrode, which may be based on the electrostatic interaction between the oxalate anion and the electrode surface. In addition, the stability of the electrochemical detection of oxalate was improved at the ATAB‐BDD electrode compared to the unmodified electrode.     

Determination of Sodium Diethyldithiocarbamate in Water by Anodic Voltammetry Using a Boron‐Doped Diamond Electrode

An electrochemical study was made of the anodic behavior of sodium diethyldithiocarbamate (DEDTC) using a boron‐doped diamond electrode (BDDE) in sodium sulfate supporting electrolyte. This paper presents a new alternative for the electroanalytical determination of DEDTC in protic media, using cyclic voltammetry or chronoamperometry. Linear plots of current vs. concentration correlated with anodic stepwise oxidation were obtained in delimited potential ranges with very good correlation coefficients.     

Voltammetric Determination of 3‐Nitrofluoranthene and 3‐Aminofluoranthene at Boron Doped Diamond Thin‐Film Electrode

The voltammetric behavior of 3‐nitrofluoranthene and 3‐aminofluoranthene was investigated in mixed methanol‐water solutions by differential pulse voltammetry (DPV) at boron doped diamond thin‐film electrode (BDDE). Optimum conditions have been found for determination of 3‐nitrofluoranthene in the concentration range of 2×10^?8–1×10^?6 mol L^?1, and for determination 3‐aminofluorathnene in the concentration range of 2×10^?7–1×10^?5 mol L^?1, respectively. Limits of determination were 3×10^?8 mol L^?1 (3‐nitrofluoranthene) and 2×10^?7 mol L^?1 (3‐aminofluoranthene).     

Simple and Feasible Simultaneous Determination of Three Phenolic Pollutants on Boron‐Doped Diamond Film Electrode

A simple, rapid and feasible method is developed for direct and simultaneous determination of phenol (Ph), hydroquinone (HQ) and 4‐nitrophenol (4‐NP) on unmodified boron‐doped diamond (BDD) electrode. Results showed that the oxidative peaks of these three phenolic compounds can be completely separated on BDD electrode in acidic conditions by using electrochemical cyclic voltammetry technique. The peak potential separations are all higher than 0.35 V. Moreover, BDD electrode is extremely easy to be refreshed to obtain current values with good reproducibility, even if it is passivated by phenolic compounds with different adsorption characteristics. All the above features are on account of the outstanding electrochemical characteristics of BDD electrode, and lead to the advantage and feasibility for simultaneous determination of three phenolic compounds without any other separation operation. For each tested phenolic compound, the concentration range with linearity is in two or three orders of magnitude in the presence of other coexisting phenolic compounds with the concentrations more than 1000 times higher than that of the tested component. The present method is also shown to be promising for the determination of phenolic contaminants in the real wastewater samples.     

Electrochemical Properties of a Boron‐Doped Diamond Electrode Modified with Gold/Polyelectrolyte Hollow Spheres

Oppositely charged polyelectrolyte (poly(allyamine hydrochloride) (PAH) and poly(sodium 4‐styrene‐sulfonate) (PSS)), and negatively charged gold nanoparticles (Au) were assembled alternately on polystyrene (PS) spheres via layer‐by‐layer technique, and the different PAH/(PSS/PAH)_n/(Au/PAH)_m/Au composite hollow spheres were derived by dissolving PS core. These hollow spheres were used to modify boron‐doped diamond (BDD) electrodes for electrochemical sensors. The cyclic voltammetric results for dopamine (DA) detection demonstrated that hollow‐sphere‐modified BDD exhibited better electrocatalytic activity than did bare BDD. Influence of the wall thickness and composition of hollow spheres on electrochemical properties were investigated. The results showed that the oxidative peak potential of DA and the peak current varied with different PSS/PAH and Au/PAH layers. The optimized wall structure of hollows spheres was PAH/(PSS/PAH)₇/(Au/PAH)₅/Au.     

Development of a Urea Bioprobe Based on Platinized Boron‐Doped Diamond Electrodes

Urea (CH₆ON₂) is one of the main human nitrogen‐based metabolic wastes. The concentration of urea in blood lies between 2.5–7 mM for healthy individuals, and is commonly used as an indicator for several diseases that may alter this value. Spectrophotometric methods are employed for the determination of blood urea concentration during clinical assays. Although these methods are sensitive, they make use of toxic reagents and complex reaction schemes. Therefore, in this research we present the bioelectrochemical determination of urea by the use of the protein urease (E.C.3.1.1.5) along with a nano‐platinized boron‐doped diamond electrode. This approach has been proven to be efficient and sensitive providing a platform with detection limits of 1.79 mM (S/N=3). The linear range resulted from 1 mM to 25 mM for the determination of urea, and response time of five minutes.     

Anodic Stripping Voltammetry of Heavy Metals at Nanocrystalline Boron‐Doped Diamond Electrode

Boron‐doped Diamond (BDD) electrode has become one of the important tools for heavy metal detection. By studying some analytical parameters of DPASV method, like deposition time and potential in different electrolyte concentrations (acetate buffer), the conditions for detecting very low metal ion levels (Zn, Cd, Pb, and Cu) could be chosen. Diluted electrolyte (0.01 M buffer) was one of the factors favoring low detection and quantification limits, but its quantification range is short in comparison to more concentrated media. For ?1.7 V deposition potential, the detection of single metal at ppb levels was reached in 60 s deposition time. Understanding different metal‐metal interactions shows the limits to the simultaneous determination of heavy metals at BDD. Quantification was possible for the simultaneous determination of Zn, Cd and Pb despite the overlapping of Zn and Cd peaks. The performance of the BDD was compared with that of another C‐based solid electrode: the glassy carbon electrode (without mercury plating). A lower base line current, wider potential range, higher sensitivity (3 to 5 times higher than GC) and longevity of the material were noticed for the BDD.     

Voltammetric Determination of Thiourea at Conductive Diamond Electrodes

The oxidation of thiourea (TU) at boron‐doped diamond (BDD) electrodes was investigated by the use of anodic voltammetry. The results indicated that the overall TU oxidation reaction is rather complicated and takes place via two steps: a slow electron‐transfer yielding the corresponding free radical, followed by a fast oxidation of this radical, prior to its dimerization. It was found that in acidic media the voltammetric response is suitable for analytical applications, and unlike glassy carbon (GC), BDD electrodes exhibit very low susceptibility to adsorption. The same conclusion was supported by the results of AC voltammetric measurements. Based upon the voltammetric peak for the first step of TU oxidation, a method is proposed for the determination of this compound in the micromolar concentration range. The analytical performance characteristics of the method are comparable to those reported for TU determination by the use of platinum electrodes or enzyme‐modified platinum electrodes.     

Simultaneous Determination of Caffeine and Acetylsalicylic Acid in Pharmaceutical Formulations Using a Boron‐Doped Diamond Film Electrode by Differential Pulse Voltammetry

This work presents a simple, fast and low‐cost method for simultaneous determination of acetylsalicylic acid (ASA), without alkaline hydrolysis and caffeine (CF) in pharmaceutical formulations using a boron‐doped diamond as the working electrode through differential pulse voltammetry. A good repeatability was reached for 20 measurements, with a low relative standard deviation of less than 1.0 %. The calibration curves presented a great linear correlation coefficient for both drugs (R=0.999) with a limit of detection of 1.6×10^?7 mol L^?1 for CF and 2.3×10^?7 mol L^?1 for ASA. The system was validated in comparison with the official method.     

Sensitive Detection of Capsaicin by Adsorptive Stripping Voltammetry at a Boron‐Doped Diamond Electrode in the Presence of Sodium Dodecylsulfate

In the present paper, a sensitive electroanalytical methodology for the determination of capsaicin using adsorptive stripping voltammetry (AdSV) at a boron‐doped diamond (BDD) electrode is presented. The voltammetric results indicate that in the presence of sodium dodecylsulfate (SDS) the BDD electrode remarkably enhances the oxidation of capsaicin which leads to an improvement of the peak current with a shift of the peak potential to less negative values. A linear working range of 0.05 to 6.0 µg mL^?1 (0.16–20 µM) with a detection limit of 0.012 µg mL^?1 (0.034 µM) has been obtained using BDD electrode by AdSV.     

Simultaneous Determination of Acetaminophen and Ascorbic Acid at an Unmodified Boron‐Doped Diamond Electrode by Differential Pulse Voltammetry in Buffered Media

A boron‐doped diamond electrode (BDDE) was used for the simultaneous anodic determination of L ‐ascorbic acid (AA) and acetaminophen (AC) in aqueous buffered media by differential pulse voltammetry (DPV). Linear calibration plots of anodic current peaks versus concentration were obtained for both analytes in the concentration range 0.01–0.1 mM with very high correlation coefficients. RSD of 2–3% and high sensitivities were obtained from DPV data in single and dicomponent systems. The potential applicability of the DPV technique associated with standard addition was illustrated by simultaneous determination of AA and AC in real sample solutions made up from pharmaceutical products.     

Electrodeposition of Lead at Boron‐Doped Diamond Film Electrodes: Effect of Temperature

The electrodeposition of lead on boron‐doped diamond has been studied with a view to identifying the fundamental parameters controlling the sensitivity and lower detection limit in anodic stripping voltammetry. Chronoamperometric transients are used to explore the deposition, indicating a progressive growth mechanism confirmed by ex situ AFM images. Linear sweep ASV experiments show a threshold concentration of ca 10^?6 M below which no lead is detected; this is attributed to the need for nucleation of the solid phase on the electrode. Experiments with variable temperature show that this threshold can be usefully lowered at elevated temperatures.     

Boron‐Doped Diamond Electrode Coupled to Liquid Chromatography: Application to Simultaneous Determination of Benzodiazepines

The applicability of boron‐doped diamond (BDD) as a working electrode in an amperometric cell, coupled to HPLC, was demonstrated, for determining benzodiazepines in pharmaceutical preparations. The separation of the benzodiazepines was achieved using a Waters XTerra RP18 column (250×4.6 mm, 5 μm) with a mobile phase sodium phosphate (pH 3.5; 0.10 mol L^?1)‐acetonitrile (65 : 35, v/v) at flow of 1.2 mL min^?1. The measurements were performed in a system 871 Advanced Bioscan (Metrohm) with a BDD (8000 ppm) adapted to the thin layer mode cell. Stainless steel and platinum wire were used as reference and auxiliary electrodes, respectively. The cell was operated in pulse mode, using ?1.9 V as initial potential. The method presented linearity, repeatability and ruggedness and it represents a novel, alternative electroanalytical method for benzodiazepines determination.     

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.