Wax-impregnated Graphite Electrode Research Articles

Highly Sensitive Sensor for the Determination of Riboflavin Using Thionine Coated Cadmium Selenide Quantum Dots Modified Graphite Electrode

In this paper, the electrochemical non-enzymatic detection of Riboflavin (RF) was proposed based on its catalytic reduction in a Thionine-coated Cadmium Selenide Quantum dots (TH@CdSe QDs)-modified paraffin wax-impregnated graphite electrode (PIGE) that was prepared using a novel approach. The synthesized TH@CdSe QDs were confirmed by UV-Vis spectroscopy, Confocal Raman Microscopy and High Resolution Transmission Electron Microscopy (HRTEM) studies. The electrochemical response of the TH@CdSe QDs-modified PIGE was studied by cyclic voltammetry. The voltammetric response of RF at the TH@CdSe QDs-modified PIGE showed higher current than the bare PIGE. Under optimum conditions, the electrocatalytic reduction currents of RF was found to be linearly related to its concentration over the range of 1.6 × 10−7 M to 1.4 × 10−4 M with a detection limit of 53 × 10−9 M (S/N = 3). The TH@CdSe QDs-modified PIGE was utilized as an amperometric sensor for the detection of RF in flow systems was performed by carrying out hydrodynamic and chronoamperometric experiments. The TH@CdSe QDs-modified PIGE showed very good stability and a longer shelf life. The applicability of the fabricated electrode was justified by the quantification of RF in commercial tablets.

Fabrication and characterization of poly 2-napthol orange film modified electrode and its application to selective detection of dopamine

The present work is based on the use of a redox mediator containing an azo group for the selective determination of dopamine in the presence of uric acid and ascorbic acid by electrochemical method. A modified electrode was prepared by electrochemical polymerization of the poly 2-napthol orange film (P2NO) on the paraffin wax-impregnated graphite electrode (PIGE) by applying potential between −0.6 and 0.8 V at scan rate of 50 mV s−1 for 30 segments. The modified P2NO film electrode was characterized by ATR-IR spectroscopy, FE-SEM, cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), differential pulse voltammetry (DPV), hydrodynamic voltammetry (HDV), and chronoamperometry (CA). The P2NO film modified electrode exhibited selective determination of dopamine in the presence of uric acid and ascorbic acid, and the electrocatalytic activity for oxidation of dopamine was excellent. The linear range for the determination of dopamine was 0.6 to 250 μM with a limit of detection of 0.13 μM. The modified P2NO electrode showed good stability and reproducibility. The modified electrode was used for real sample analysis such as human blood serum, rat blood serum, and pharmaceutical samples (dopamine hydrochloride injection). The results obtained were found to be satisfactory.

Electrochemical sensing of hydroxylamine using a wax impregnated graphite electrode modified with a nanocomposite consisting of ferric oxide and copper hexacyanoferrate

The authors describe a wax-impregnated graphite electrode modified with ferric oxide (Fe2O3) and copper hexacyanoferrate(II), and its application as an electrochemical sensor for hydroxylamine. The presence of Fe2O3 nanoparticles enhance the electron transfer kinetics and electrocatalytic activities, and also enlarge the surface area of the modified electrode. As compared to the unmodified electrode, 16.9 and 30.1 fold enhancements in amperometric response was observed for copper hexacyanoferrate(II) and the nanocomposite modified electrodes, respectively. Also, the presence of Fe2O3 in the nanocomposite enhances the anodic current response by 1.78 fold when compared to copper hexacyanoferrate(II) alone modified electrode. The electron transfer coefficient, electron transfer rate constant, diffusion coefficient and catalytic rate constant for the electro-oxidation of hydroxylamine were determined. Amperometry performed at a working voltage of 750 mV (vs. Ag/AgCl) revealed a detection range that extends from 0.8 μM to 100 μM, a detection limit of 0.5 μM (at an S/N ratio of 3) and a sensitivity of 0.0924 mA⋅mM−1. The modified electrode is remarkably stable and was successfully applied to the determination of hydroxylamine in spiked water samples.

Facile immobilization of potassium-copper hexacyanoferrate nanoparticles using a room-temperature ionic liquid as an ionic binder and its application towards BHA determination

In this paper, a facile immobilization of copper hexacyanoferrate nanoparticles (CuHCFNP) on a paraffin wax-impregnated graphite electrode (PIGE) was carried out using the room-temperature ionic liquid (RTIL) 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF4) as an ionic binder. The characteristics of the CuHCFNP/EMIMBF4 gel-modified electrode were investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) techniques, and the modified electrode morphology was also characterized using field emission scanning electron microscopy (FESEM). The electrocatalytic behavior of butylated hydroxyl anisole (BHA) at the modified electrode has been investigated in 0.1 M KNO3 in static and dynamic conditions. Under the optimum conditions, the oxidation peak current was proportional to the BHA concentration in the range from 1.5 to 1000 μM with a detection limit of 0.5 μM (S/N = 3). The proposed method was applied to determine BHA content in real samples with satisfactory results.

Cathodic electrochemiluminescence of the peroxydisulphate–ciprofloxacin system and its analytical applications

The cathodic electrochemiluminescence (ECL) of peroxydisulphate (S(2)O(8)(2-))-ciprofloxacin (CPF) system at a wax-impregnated graphite electrode was studied. When CPF was absent, S(2)O(8)(2-) was electrochemically reduced to sulphate free radical (SO(4)(•-)), and dissolved oxygen absorbed on the electrode surface was reduced to protonated superoxide anion radical (HO(2)(•)). The HO(2)(•) was oxidized by SO(4)(•-) to produce molecular oxygen in both singlet and triplet states. Some of the singlet molecular oxygen ((1)O(2)) further combined through collision to be an energy-rich precursor singlet molecular oxygen pair ((1)O(2))(2). A weak ECL was produced when (1)O(2) or ((1)O(2))(2) was converted to ground-state molecular oxygen ((3)O(2)). When CPF was present, a stronger ECL was produced, which originated from two emitting species. The main emitting species was excited state CPF (CPF*), which was produced by accepting energy from ((1)O(2))(2). The other emitting species was excited singlet molecular oxygen pair [((1)O(2))(2)*], which originated from the chemical oxidation of CPF by SO(4)(•-) and dissolved oxygen. Based on the stronger ECL phenomenon, an ECL method for the determination of either S(2)O(8)(2-) or CPF was proposed. The proposed ECL method has been applied to the determination of CPF in pharmaceutical preparations.

Sodium dodecyl sulfate sensitized electrochemical method for subnanomole level determination of ortho-phenylphenol at a novel disposable electrode

The electrochemical behavior of ortho-phenylphenol (OPP) at a disposable electrode (an improved wax-impregnated graphite electrode) in the presence of sodium dodecyl sulfate (SDS) was studied for the first time. The results demonstrated that the electrocatalytic oxidation process of OPP was accompanied with two-charge-two-proton transference. The electronic transmission coefficient (α) and diffusion coefficient (DR) for OPP were calculated to be 0.8126 and 3.61 × 10−2 cm2/s, respectively. The electrochemical signal was apparently improved by SDS at the disposable electrode and the oxidative peaks current was proportional to the concentration of OPP over the range from 1.0 × 10−9 to 4.0 × 10−6 mol/L with the detection limit of 8.7 × 10−10 mol/L. This novel and highly sensitive method can be successfully applied to detect OPP in the orange rind sample.

Simultaneous determination of ultratrace lead and cadmium by square wave stripping voltammetry with in situ depositing bismuth at Nafion-medical stone doped disposable electrode

An ultrasensitive electrochemical method for simultaneous determination of lead and cadmium was first developed using the novel bismuth–Nafion-medical stone doped disposable electrode (an improved wax-impregnated graphite electrode). Through the synergistic sensitization effect of the resulting composite material, the disposable electrode showed remarkable electrochemical responses to lead and cadmium. The oxidation of the two metals produced two well-defined and separated square wave peaks at about −0.62 V for Pb 2+ and −0.85 V for Cd 2+, respectively. The effects of the amount of medical stone, concentration of Nafion, thickness of bismuth, pH of buffer solution, deposition potential, accumulation time, voltammetric measurement and possible interferences were investigated in detail. Under the optimal conditions, the fabricated electrode exhibited linear ranges from 2.0 to 12.0 μg L −1 with detection limit of 0.07 μg L −1 for lead and 2.0–12.0 μg L −1 with detection limit of 0.47 μg L −1 for cadmium. The assay results of heavy metals in wastewater with the proposed method were in acceptable agreement with the atomic absorption spectroscopy method.

Sodium dodecyl sulfate sensitized electrochemical method for sub-picomole level determination of topotecan hydrochloride at a novel disposable electrode

A sub-picomole level topotecan hydrochloride determination method was first proposed using sodium dodecyl sulfate (SDS) as a sensitized reagent at a novel disposable electrode (an improved wax-impregnated graphite electrode). The effects of different kinds of surfactants on the electrochemical response to topotecan hydrochloride were examined. The results indicate the electrochemical signal was apparently improved by SDS. At optimal conditions, the oxidative peak current increased linearly with the logarithm of concentrations for topotecan hydrochloride in the ranges of 2.0 × 10−12 to 1.0 × 10−11 mol/L and 8.0 × 10−11 to 8.0 × 10−10 mol/L with a detection limit of 6.4 × 10−13 mol/L. The proposed method could be applied in determining topotecan hydrochloride in urine.

A quercetin-modified biosensor for amperometric determination of uric acid in the presence of ascorbic acid

The present work reports a quercetin-modified wax-impregnated graphite electrode (Qu/WGE) prepared through an electrochemical oxidation procedure in quercetin-containing phosphate buffer solution (PBS), for the purpose of detecting uric acid (UA) in the presence of ascorbic acid (AA). During modification quercetin was oxidized to the corresponding quinonic structure, and in the blank buffer solution the electrodeposited film exhibits a voltammetric response anticipated for the surface-immobilized quercetin. Retarding effect of the film towards the reaction of anionic species was found; therefore the pH of sample solutions was selected to ensure the analyte in molecular form. At suitable pHs the Qu/WGE shows excellent electrocatalytic effect towards the oxidation of both AA and UA, and separates the voltammetric signal of UA from AA by about 280 mV, allowing simultaneous detection of these two species. A linear relation between the peak current and concentration was obtained for UA in the range of 1–50 μM in the presence of 0.5 mM AA, with a detection limit 1.0 μM ( S/ N = 3). This sensor was stable, reproducible and outstanding for long-term use.

Multilayer films of cationic surfactants incorporating polyoxometalate on electrodes

A new kind of multilayer of didodecyldime- thylammonium bromide (DDAB) and 1:12 phospho- molybdic anions (PMo12) was achieved on the surface of a wax-impregnated graphite (WIG) electrode by ion exchange and electrostatic interaction. The character- ization and electrochemical behavior of the multilayer films of DDAB/PMo12 is described in detail. The chemically modified electrode was shown to exhibit an excellent electrocatalytic activity toward the reduction of BrO3 - anion in 0.5 M H2SO4 and possesses several attractive features, such as simple preparation, fast response, good stability, etc.

Inorganic–organic hybrid polyoxometalate nanoparticle modified wax impregnated graphite electrode: preparation, electrochemistry and electrocatalysis

A kind of inorganic–organic hybrid polyoxometalate (POM) nanoparticle [(CH 3) 4N] 6P 2Mo 18O 62 · 9H 2O has been designed and prepared by solid-state reaction at room temperature and immobilized on the surface of a wax impregnated graphite electrode (WIGE) by the sol–gel technique for the first time. The electrochemical behavior of the [(CH 3) 4N] 6P 2Mo 18O 62 · 9H 2O nanoparticle modified WIGE (P 2Mo 18-WIGE) has been studied in detail, including pH-dependence, solvent effect and stability. The electrocatalytic behavior of the P 2Mo 18-WIGE toward the reduction of chlorate, hydrogen peroxide and nitrite in 1 M H 2SO 4 aqueous solution is reported. The experimental results show that the P 2Mo 18-WIGE not only maintains the electrochemical activity and electrocatalytic properties of the H 6P 2Mo 18O 62, but also shows remarkable stability due to insolubility of the hybrid POM nanoparticles, which is important for practical applications. The significance of our research work is to provide a kind of novel and very stable POM-based solid nano-material applied in electrode modification.

Field-based comparison of platinum and wax impregnated graphite redox electrodes

An inert electrode was constructed using wax-impregnated graphite (WIG) as an alternative to Pt for permanent installation in the regolith. The performance of WIG electrodes has not previously been systematically evaluated by using data from field trials, although Pt and WIG measure similar Eh values in laboratory solutions. We compared the performance of the WIG electrode when installed adjacent to Pt redox electrodes in the A, B and C horizons of duplex soils in a X-eralf-Aqualf toposequence near Mount Crawford in the Mt Lofty Ranges, South Australia. Lower potentials, commonly in the order of 200 mV, were measured from WIG electrodes, relative to Pt electrodes. Measurements of potential from adjacently installed WIG and Pt electrodes did not show significant correlation. Generally oxidizing redox potentials were measured in all soils in which electrodes were installed due to below average rainfall during the sampling period. Further testing of WIG electrodes in reduced regolith is needed. Interpretation of Eh trends, measured using Pt electrodes, between the A, B and C horizon are presented.

Determination of cyanide using a tyrosinase amperometric biosensor with catechol as substrate

Low cyanide concentrations are determined with a tyrosinase amperometric biosensor using enzyme immobilized on a preactivated polyamide membrane that is closely attached to the end of a wax-impregnated graphite electrode. The test is performed in the presence of the catechol substrate at –0.200 V versus SCE in 0.1 mol l–1 phosphate buffer (pH 7.5)(the reduction current results from o-benzoquinone, derived from the tyrosinase driving the oxidation of catechol, which is being measured). The decrease in substrate response within the linear range 2.0 × 10–7–;4.0 × 10–5 mol l–1 is proportional to the square-root of cyanide concentration. This method is characterized by high selectivity and reproducibility.

Determination of Captropril using adsorptive cathodic differential pulse stripping voltammetry with the HMDE

A voltammetric method for the determination of 3-mercapto-D-2-methylpropanoyl-L-proline, a hypotensive drug whose pharmaceutical name is Captopril (CPT), in the concentration range from 9.0×10 −10 M to 3×10 −6 M, is described. In this range the peak current increases linearly with drug concentration even when different collection periods are used. A self-cleaning Hanging Mercury Drop Electrode (HMDE) was used and a negative Differential Pulse potential (DP) was applied to the indicator electrode. The stripping peak of CPT splits into two peaks as soon as the concentration is increased over about 10 −5 M; in the oxidation DP scan, instead, this splitting is observed at a concentration of 2.0×10 −4 M. Some attempts were made to verify the suitability of other techniques such as Alternating Current polarography (AC) and the use of a different electrode, the Wax-Impregnated Graphite Electrode (WIGE).

Preconcentration of tranquilizers by adsorption/extraction at a wax-impregnated graphite electrode

The tranquilizers promethiazine, diethazine, trifluoperazine, fluphenazine and clozapin adsorb at the surface and extract into the wax-impregnated graphite electrode (WIGE) as shown by chronocoulometry. Extraction/adsorption at the electrode serves as a preconcentration step which improves the limit of detection for the drugs by differential pulse voltammetry. A 15-min preconcentration gave a linear range of 10 −4–5 × 10 −8 M with a detection limit of 5 × 10 −9 M for clozapin in pH 7 phosphate buffer. The determination of tranquilizers in urine and plasma required no preliminary treatment; the detection limits were 5 × 10 −8 M in urine and 10 −7 in plasma. Plasma measurements were made at a WIGE covered with a Spectrapor membrane to prevent electrode fouling by protein adsorption.

Graphite electrode for the measurement of redox potential and oxygen diffusion rate in soil

The objective of this study was to evaluate wax impregnated graphite electrodes (WIGEs) and platinum wire electrodes (PWEs) in the determination of two oxygen indicators: oxygen diffusion rate (ODR) and redox potential (Eh). These determinations were made in aqueous solutions, soil suspensions, and moist soil. In aqueous solutions, WIGEs had greater current efficiencies and a wider current plateau than PWEs. The response of both electrodes to increasing concentrations of dissolved oxygen was linear. In soil, the current-plateau region for both electrodes was a function of the soil moisture content. The response for both electrodes to increasing concentrations of oxygen in the soil was linear to about 60%. For redox measurements, the WIGEs gave excellent agreement, but the PWEs showed significant variation with the Nernst equation in a well-poised solution. In a buffered solution both electrodes performed well. This work has shown that WIGEs are less susceptible to poisoning by oxides, can be fabricated easily, are relatively inexpensive, are more stable in the soil than PWEs, and have a greater sensing area. In monitoring of hazardous waste land disposal sites, WIGEs can be substituted for PWEs whenever determinations of ODR and redox are made.

Redox potential and oxygen diffusion rate as parameters for monitoring biodegradation of some organic wastes in soil

Wax impregnated graphite electrodes (WIGEs) and platinum wire electrodes (PWEs) have been used to monitor the redox potential ( E H ) and the oxygen diffusion rate (ODR) during biodegradation of glucose and phenol in a soil environment. The microbial activity and the actual degradation of these compounds also were determined analytically, and the results were compared with the E H and ODR measurements. The results show that E H and ODR can be suitable parameters for the indication of complete biodegradation of organic wastes by land treatment.

Stripping chronocoulometry for the determination of pertechnetate

Stripping chronocoulometry is proposed as an alternative to linear-sweep anodic stripping voltammetry when the latter technique gives multiple stripping waves. Such complicated stripping waves are commonly observed at solid electrodes. The determination of pertechnetate ( 99Tc) demonstrates the advantages of stripping chronocoulometry at a wax-impregnated graphite electrode.

Preconcentration of chlorpromazine at a wax-impregnated graphite electrode

Summary Chlorpromazine is shown to extract from aqueous sample solutions into a waximpregnated graphite electrode (WIGE). Chronocoulometry gives a charge—time curve with an intercept that indicates adsorption of chlorpromazine at the interface and a time dependence consistent with chlorpromazine extraction into the WIGE. The extraction serves as a preconcentration step which lowers the detection limit for chlorpromazine when determined by differential pulse voltammetry.

Thin-layer differential pulse voltammetric determination of chlorpromazine in biological fluids

The combination of a thin-layer electrochemical cell with differential pulse voltammetry can be used to determine chlorpromazine in plasma and urine. The thin-layer cell (23 μl capacity) has a wax-impregnated graphite electrode. Direct determination of chlorpromazine in urine gave a linear calibration curve for the range 4.8 × 10 -3–2.4 × 10 -4 M with 97% recovery. No interference from glutethimide, dextropropoxyphene, meprobamate, diazepam, and methaqualone-HCl was detected. Direct measurement of chlorpromazine in plasma gave a linear calibration curve for the range 2.4 × 10 -5–4.8 × 10 -4 M with 89% recovery. The procedure for plasma and urine requires only 2 min per determination. Detection levels are below that required for monitoring therapeutic levels of chlorpromazine in urine.