Application of anodized edge-plane pyrolytic graphite electrode for analysis of clindamycin in pharmaceutical formulations and human urine samples

Different graphitic carbon-based electrode materials were evaluated for direct electro-oxidation of clindamycin and electroanalytical parameters such as sensitivity, residual background current, and signal-tobackground current ratio were compared to select the best one for the clindamycin electroanalysis. Such electrode materials include glassy carbon, carbon paste, pyrolytic graphite (edge-plane and basal-plane), carbon nanotube, reduced graphene oxide, and carbon black. The edge-plane pyrolytic graphite electrode after a simple and fast electrochemical pretreatment showed superior performance compared with the other carbon electrodes. Raman and Fourier transform infrared spectroscopy were employed to analyze the surface microstructure and chemical bonding of the carbon materials and scanning electron microscopy was used to study their surface morphologic features. The applicability of the electrochemically activated edge-plane pyrolytic graphite electrode for the determination of clindamycin in pharmaceutical formulations and human urine samples was evaluated.     

Exploration of gas sensing possibilities with edge plane pyrolytic graphite electrodes: nitrogen dioxide detection

The voltammetric response of nitrogen dioxide in aqueous sulfuric acid using an edge plane pyrolytic graphite electrode has been explored and contrasted with that from basal plane pyrolytic graphite, glassy carbon or boron-doped diamond electrodes. Edge plane graphite electrode is found to produce an excellent voltammetric signal in comparison with other carbon-based electrodes exhibiting a well-defined analytically useful voltammetric redox couple in 2.5 M sulfuric acid which is absent on the alternative electrodes.     

A Comparison of Edge-plane and Basal-plane Pyrolytic Graphite Electrodes towards Sensitive Determination of the Fungicide Mandipropamid

A sensitive square-wave voltammetry (SWV) method based on basal-plane pyrolytic graphite electrode (BPPGE) and edge-plane pyrolytic graphite electrode (EPPGE) was developed to determine the concentration of the pesticide mandipropamid (MAN) in spiked river water and grape juice samples. Under optimal experimental conditions, the SWV response of EPPGE and BPPGE was linear over the concentration ranges of 0.7 to 9.0 μmol L⁻¹ and 0.5 to 10.0 μmol L⁻¹, respectively. The method was successfully used to determine MAN in spiked samples with good recovery. Cyclic voltammetry (CV) was conducted to understand the mechanism underlying the electrode process of MAN.     

聚酚藏花红功能碳纳米管生物阳极制备及其在乙醇传感器应用

应用电化学法聚合酚藏花红（PPS）功能化的单壁碳纳米管,以其作为烟酰胺辅酶（NADH）氧化的电化学催化剂（电极）,构建基于乙醇脱氢酶的安培型乙醇生物电化学传感器.该电极于0.0 V时,对NADH具有很好的催化性能.而单体酚藏花红则由于其电位过低（-0.48 V）,不能显示催化性能.循环伏安和计时安培法测试表明：该传感器...     

Electrochemical determination of sulfide at various carbon substrates: a comparative study.

The direct electrochemical oxidation of sodium sulfide has been examined at five different carbon-based electrode substrates (glassy carbon (GC), boron-doped diamond (BDD), edge-plane pyrollytic graphite (EPPG), basal-plane pyrollytic graphite (BPPG) and carbon nanotubes (CNT)). An electrocatalytic response is observed at both the EPPG and CNT electrode compared to that of the other three substrates. The higher capacitative charging currents obtained at the CNT electrode hinder its detection range and, as such, the EPPG electrode has been clearly shown to be the substrate of choice for the direct electrochemical detection of sulfide. The procedure was applied to the recovery of a sulfide spike in river water, with a recovery of 104%.     

Edge Plane Pyrolytic Graphite Electrodes for Stripping Voltammetry: a Comparison with Other Carbon Based Electrodes

The first examples of using edge plane pyrolytic graphite electrodes for anodic and cathodic stripping voltammetry (ASV and CSV) are presented, notably the ASV of silver and the CSV of manganese. In the former example, detection limits for silver (based on 3σ) of 8.1 nM and 0.185 nM for 120 s and 300 s accumulation time, respectively, were achievable using the edge plane electrode, which were superior to those observed on glassy carbon, basal plane pyrolytic graphite and boron‐doped diamond electrodes. In the second example, a detection limit for manganese of 0.3 μM was possible which was comparable with that achievable with a boron‐doped diamond electrode but with an increased sensitivity. Comparison of the edge plane pyrolytic graphite electrode with boron‐doped diamond electrodes reveals that the edge plane electrode has comparable detection limits and sensitivities whilst exhibiting a lower signal‐to‐noise ratio and large potential window for use in trace analysis suggesting boron‐doped diamond can be conveniently replaced by edge plane pyrolytic graphite as an electrode material in many applications.     

Tetracyanoquinodimethane (TCNQ) modified electrode for NADH oxidation

A TCNQ-modified edge-plane pyrolytic graphite electrode prepared by a dip-coating procedure shows electrocatalytic activity for NADH oxidation in phosphate buffer solutions (pH 7.0). The modified electrode is stable and shows a linear relation for NADH in the concentration range 1–10 mM. The rate constant between adsorbed TCNQ and NADH in solution has been estimated to be 1.46 × 10⁶ M⁻¹s⁻¹ at 25°C. The modified electrode has the potential use as a sensor for dehydrogenase-enzyme-based substrates.     

A comparison of edge- and basal-plane pyrolytic graphite electrodes towards the sensitive determination of hydrocortisone

Electrochemical sensor employing edge-plane pyrolytic graphite electrode (EPPGE) for the sensitive detection of hydrocortisone (HC) is delineated for the first time. The electrochemical properties are investigated exercising the cyclic voltammetry and square-wave voltammetry (SWV). When equating with the bare basal-plane pyrolytic graphite electrode (BPPGE), the EPPGE gave better response towards the detection of HC both in terms of sensitivity and detection limit. The voltammetric results indicated that EPPGE remarkably enhances the reduction of HC which leads to considerable amelioration of peak current with shift of peak potential to less negative values. The difference in the surface morphology of two electrodes has been studied. Also, the EPPGE delivered an analytical performance for HC with a sensitivity of 45 nA nM⁻¹ and limit of detection of 88 nM in the concentration range 100-2000 nM. The method has been utilized for the determination of HC in pharmaceuticals and real samples. The electroanalytical method using EPPGE is the most sensitive method for determination of HC with lowest limit of detection to date. The major metabolites present in blood plasma did not intervene with the present investigation as they did not exhibit reduction peak in the experimental range used. A comparison of results with high performance liquid chromatography (HPLC) signalizes a good agreement.     

Direct Electrooxidation of Ascorbic Acid at the Nanocrystaline Graphite‐like Pyrolytic Carbon Film Electrode

Pyrolytic carbon films (PCFs) were prepared by chemical vapor deposition (CVD) at different deposition temperatures. As an example of using PCF electrode in electroanalysis, the direct electrooxidation of ascorbic acid (AA) at the PCF electrode was investigated and compared with common carbon‐based electrodes such as glassy carbon (GC), edge plane pyrolytic graphite (EPPG), and basal plane pyrolytic graphite (BPPG) electrodes. It was found that the PCF electrodes prepared under deposition temperatures higher than 1050 °C showed a higher sensitivity and lower overpotential compared to the other carbon electrodes. The electrode was successfully applied for determination of AA in real samples.     

A simple electroanalytical methodology for the simultaneous determination of dopamine,serotonin and ascorbic acid using an unmodified edge plane pyrolytic graphite electrode

A simple method using an unmodified edge plane pyrolytic graphite electrode (EPPGE) is reported for the simultaneous determination of dopamine (DA), serotonin (ST) and ascorbic acid (AA). The performance of this electrode is superior to other unmodified carbon-based electrodes and also to many modified electrodes in terms of detection limit, sensitivity and peak separation for determination of DA, ST and AA. Using this method, detection limits of 90 nM, 60 nM and 200 nM were obtained for DA, ST and AA respectively. No electrode fouling is observed during a set of experiments and good sensitivity is obtained for the simultaneous determination of DA, ST and AA. The peaks for the three species are well resolved from each other and the electrode is successfully utilised for their determination in standard and real samples.      

A Comparison of Electron Transfer Kinetics of Three Common Carbon Electrode Surfaces in Acetonitrile and in Room Temperature Ionic Liquid 1‐Butyl‐3‐Methylimidiazonium Hexafluorophosphate: Correlation to Surface Structure and the Limit of the Diffusion Domain Approximation

We report the comparison of electron transfer kinetic parameters of the ferrocene redox couple in both acetonitrile and in room temperature ionic liquid (RTIL) 1‐butyl‐3‐methylimidiazonium hexafluorophosphate ([C₄mim] [PF₆]), using edge plane pyrolytic graphite (EPPG), basal plane pyrolytic graphite (BPPG) and glassy carbon (GC) electrodes. Each electrode surface was characterized using SEM and AFM and the surface morphology was analyzed in terms of surface heterogeneity including the distribution of edge plane defects. The experimental data were modeled using both one and two dimensional simulations to correlate the electron transfer parameters obtained with the different surface structure of each electrode. Furthermore, we show that the diffusion domain approximation (commonly used to accurately simulate electron transfer kinetics at graphitic surfaces) breaks down when a BPPG electrode is used in RTIL and demonstrate the near impossibility of assigning rate constant to the basal plane surface.     

Edge Plane Pyrolytic Graphite Electrodes for Halide Detection in Aqueous Solutions

The behavior of chloride, bromide and iodide at edge plane pyrolytic graphite electrodes has been explored in aqueous acid solutions. The voltammetric response in each case has been compared with that of basal plane pyrolytic graphite, glassy carbon and boron‐doped diamond. The electrochemical oxidation of chloride is found to only occur on boron‐doped diamond while the electrochemical reversibility for the oxidation of bromide on edge plane pyrolytic graphite is similar to that seen at glassy carbon whilst being superior to basal plane pyrolytic graphite and boron‐doped diamond. In the case of iodide oxidation, edge plane and basal plane pyrolytic graphite and glassy carbon display similar electrode kinetics but are all superior to boron‐doped diamond. The analytical possibilities were examined using the edge plane pyrolytic graphite electrode for both iodide and bromine where is was found that, based on cyclic voltammetry, detection limits in the order of 10^?6 M are possible.     

Direct Oxidation of Ascorbic Acid at an Edge Plane Pyrolytic Graphite Electrode: A Comparison of the Electroanalytical Response with Other Carbon Electrodes

The direct electrochemical oxidation of ascorbic acid at an edge plane pyrolytic graphite electrode (EPPG) is investigated and compared with other common carbon‐based electrodes, specifically glassy carbon, boron doped diamond and basal plane pyrolytic graphite. It is found that the EPPG electrode shows a significantly higher degree of electrochemical reversibility than the other electrode substrates giving rise to an analytically optimized limit of detection and sensitivity of 7.1×10^?5 M and 0.065 A M^?1 respectively.     

Apparent 'electrocatalytic' activity of multiwalled carbon nanotubes in the detection of the anaesthetic halothane: occluded copper nanoparticles

The electrocatalytic detection of the anaesthetic halothane on a multiwalled carbon nanotube modified glassy carbon electrode is reported with a low limit of detection of 4.6 microM. A thorough investigation of the underlying cause of this apparent catalytic effect is undertaken by comparing the response of various carbon electrodes including glassy carbon, basal- and edge-plane pyrolytic graphite electrodes (bppg and eppg respectively) to increasing additions of halothane. The reduction of halothane is shifted by 250-300 mV to more negative potentials at an eppg electrode than that observed at the GC-CNT electrode. Therefore the results of this investigation show that, surprisingly, the electrocatalysis is not solely due to the introduction of edge-plane-like defect sites on the carbon nanotubes as is commonly found for many other substrates showing favourable voltammetry at nanotube modified electrodes. Instead, we reveal that in this unusual case the electroactive sites for the reduction of halothane are due to the presence of copper nanoparticles occluded within the carbon nanotubes during their production, which are never completely removed by standard purification techniques such as acid washing. This is only the third known case where apparent electrocatalysis by carbon nanotube modified electrodes is due to occluded metal-related nanoparticles within the nanotube structure, rather than the active sites being the edge-plane-like defect sites on the nanotubes. Furthermore this is the first case where the active sites are nanoparticles of copper metal, rather than metal oxide nanoparticles (namely oxides of iron(II)/(III)) as was found to be the case in the previous examples.     

CVD graphene vs. highly ordered pyrolytic graphite for use in electroanalytical sensing

We explore and contrast the electroanalytical performance of a commercially available CVD grown graphene electrode with that of edge- and basal-plane pyrolytic graphite electrodes constructed from highly ordered pyrolytic graphite for the sensing of biologically important analytes, namely β-nicotinamide adenine dinucleotide (NADH) and uric acid (UA). We demonstrate that for the analytes studied here, in the best case, the electroanalytical performance of the CVD-graphene mimics that of edge plane pyrolytic graphite, suggesting no significant advantage of utilising CVD-graphene in this context.     

Application of Nanocrystalline Graphite‐like Pyrolytic Carbon Film Electrode in the Electroanalytical Determination of Famotidine

Direct electro‐oxidation of famotidine at different graphitic carbon‐based electrode materials was evaluated. These materials included conventional electrodes of edge‐plane pyrolytic graphite, basal‐plane pyrolytic graphite, carbon paste, and glassy carbon as well as nano‐structured carbon‐based materials such as pyrolytic carbon film, carbon nanotube, and nano‐graphene. Raman spectroscopy and scanning electron microscopy were employed to analyze their structural and morphological features. It was found that the pyrolytic carbon film electrode, after a simple and fast anodic activation, shows superior electroanalytical performance. The method was successfully applied for the electroanalytical determination of famotidine in tablet dosage forms and urine samples.     

Electroanalytical determination of cadmium(II) and lead(II) using an in-situ bismuth film modified edge plane pyrolytic graphite electrode.

A highly sensitive and simple electroanalytical methodology is presented using an in-situ bismuth film modified edge plane pyrolytic graphite electrode (BiF-EPPGE) which is exemplified with the simultaneous determination of cadmium(II) and lead(II). Square-wave anodic stripping voltammetry is utilised with the effects of several experimental variables studied. Simultaneous additions of cadmium(II) and lead(II) were investigated where two linear ranges between 0.1-100 and 0.1-300 microg/L and also detection limits of 0.062 and 0.084 microg/L were obtained, respectively. The method was then successfully applied to the simultaneous determination of cadmium(II) and lead(II) in spiked river water, where recoveries of 100.5 and 98% were obtained, respectively. This electroanalytical protocol using edge plane pyrolytic graphite electrodes is one of the simplest methodologies to date using non-mercury based electrodes and is simpler and cheaper than alternatives such as carbon nanotube electrode arrays, suggesting the use of edge plane pyrolytic graphite electrode for routine sensing.     

Insights into the electro-oxidation of hydrazine at single-walled carbon-nanotube-modified edge-plane pyrolytic graphite electrodes electro-decorated with metal and metal oxide films

Electrochemistry of edge-plane pyrolytic graphite electrodes (EPPGEs) modified with Aldrich single-walled carbon nanotubes (SWCNTs) electro-decorated with metal (Ni, Fe and Co) and their oxides have been studied. The morphology and identity of the metallic dispersions were examined by scanning electron microscopy and energy-dispersive spectroscopy. We show that SWCNTs serve as efficient conducting carbon material for electronic communication between metal films and the underlying carbon electrode. By using cyclic voltammetry and electrochemical impedance spectroscopy (EIS) techniques, it is proved that both EPPGE-SWCNT-Ni and EPPGE-SWCNT-Fe exhibit comparable electrochemical response in buffered aqueous solution (pH 7.0) and towards electro-oxidation of hydrazine in Na₂SO₄ solution. The impedance spectra of these SWCNT-metal hybrids were complicated and follow electrical equivalent circuit model typical of adsorption-controlled charge transfer kinetics. Hydrazine impedance spectra exhibited inductive loop, characteristic of Faradaic current being governed by the occupation of an intermediate state. On the other hand, the EIS data obtained in a simple redox probe, [Fe(CN)₆]³⁻/[Fe(CN)₆]⁴⁻, showed that EPPGE-SWCNT and EPPGE-SWCNT-Ni followed electrical equivalent circuit models typical of partial charge transfer or adsorption-controlled kinetics with some resemblance to the behaviour of electrolyte–insulator–semiconductor sensors.     

Quasi in situ XPS study of anion intercalation into HOPG from the ionic liquid [EMIM][BF4]

Highly oriented pyrolytic graphite (HOPG) electrodes were electrochemically oxidized in the ionic liquid [EMIM][BF₄]. Both, the electrolyte and the electrode surface were investigated using X-ray photoelectron spectroscopy (XPS) after electrochemical treatment. For that purpose an electrochemical preparation chamber was attached to the ultra high vacuum system allowing for preparation of electrodes in non-aqueous electrolyte and subsequent sample transfer under inert nitrogen atmosphere. The XP-spectra of all species detected on the oxidized HOPG surface show core level shifts towards lower binding energies referring to a Fermi level shift and proving that a graphite intercalation compound was formed. Anion intercalation occurs together with co-intercalation of cations at 2 V vs. carbon quasi-reference electrode and is found to be irreversible. XPS analysis of the ionic liquid prior to and after electrochemical treatment indicates a change in electrolyte composition.     

Molecular Oxygen Reduction Electrocatalyzed by meso-Substituted Cobalt Corroles Coated on Edge-Plane Pyrolytic Graphite Electrodes in Acidic Media

Five meso-substituted cobalt(III) corroles were examined as to their catalytic activity for the electoreduction of O(2) when coated on an edge-plane pyrolytic graphite electrode in 1.0 M HClO(4). The investigated compounds are represented as (TpRPCor)Co(PPh(3)), where TpRPCor is the trianion of a para-substituted triphenylcorrole and R = OMe, Me, H, F, or Cl. Three electrochemical techniques, cyclic voltammetry, linear sweep voltammetry with a rotating disk electrode (RDE), and voltammetry at a rotating ring disk electrode (RRDE), were utilized to evaluate the catalytic activity of the corroles in the reduction of O(2). Cobalt corroles containing electron-withdrawing substituents were shown to be better catalysts than those having electron-donating groups on the three meso-phenyl rings of the triarylcorroles.