GCE Surface Research Articles

Electrochemical sensor based on multi-walled carbon nanotubes–boehmite nanoparticle composite modified electrode

A sensitive electrochemical sensor was developed for the analysis of dobutamine (Dob) using a glassy carbon electrode modified with multi-walled carbon nanotubes–boehmite nanoparticle composite (BNP–MWNTs/GCE). Scanning electron microscopy was used for the characterization of synthesized BNPs and the morphology of BNP–MWNTs on the surface of GCE. Under the optimized experimental conditions, the BNP–MWNTs/GCE exhibited higher peak current than bare GCE due to synergetic effect of BNPs and MWCNTs on the electrochemical oxidation of Dob. The effect of various experimental parameters such as pH, scan rate, accumulation time on the voltammetric response of Dob was studied and optimized. A wide linear range from 0.005 to 1.0 µM with a low detection limit of 8.9 nM was found for voltammetric quantification of Dob. The prepared sensor exhibited the acceptable repeatability, high reproducibility along with good stability which makes it appropriate candidate for determination Dob in pharmaceutical preparations.

Methylparaben quantification via electrochemical sensor based on reduced graphene oxide decorated with ruthenium nanoparticles

MePa quantification was performed through an electroanalytical method, in which the presence of rGO/RuNPs on GCE surface allowed the increase of the charge transfer rate in the oxidation process of the target molecule. The characterization of the composite material was carried out by TEM, in which the presence of RuNPs with an average diameter of 3.1±0.5nm dispersed on the surface of rGO was observed.The electroanalytical method developed showed a linear response range of 5.00×10−7–3.00×10−6molL−1 and LOD of 2.40×10−7molL−1. The results were statistically compared with the data obtained by the official method (HPLC) and shown to be equivalent, which allows discussion upon the use of electroanalytical methods of alternative forms of official analysis methods in cosmetic samples.

A facile one-pot hydrothermal synthesis of tin sulfide-decorated reduced graphene oxide nanoribbons and its sensing application for a flavanone naringenin

New electrode materials have been synthesized extensively with the aim of enhancing sensitivity and selectivity besides decreasing the overpotential of electrode reactions. Present work describes the design of a new one-pot hydrothermal route for the preparation of highly electroactive nanocomposite, SnS2 decorated reduced graphene oxide nanoribbons (designated as SnS2-rGONRs) for analytical and binding applications of a flavanone, naringenin (NAR). Electrode materials were characterized by XRD, Raman, TEM and AFM techniques. SnS2-rGONRs based electrochemical sensor was fabricated by drop casting of SnS2-rGONRs dispersion on GCE surface (SnS2-rGONRs/GCE). SnS2-rGONRs/GCE was utilized to explore the detailed electrochemistry of NAR and to unravel the mechanism of interaction of NAR with human serum albumin. About 50-fold enhancement in the electrochemical response of NAR was observed at SnS2-rGONRs/GCE compared to that noticed at bare GCE, suggesting that the interface SnS2-rGONRs has an excellent charge transfer capability. Influence of pH and scan rate was studied to explore the electrode kinetics of NAR. Under the optimized conditions, a linear relationship between the peak current and concentration of NAR was observed in the range of 0.49–56.6μM. Proposed electrode, SnS2-rGONRs/GCE was employed for the determination of NAR in analyte fortified biological samples. Binding characteristics viz., binding constant, stiochiometry and mode of interaction of NAR with drug carrier protein, human serum albumin (HSA) was also explored using the proposed sensor. Binding constant of NAR-HSA was found to be in the order of 104M−1 and one molecule of NAR was bound to one macromolecule of HSA.

Development of WO3 Nanoparticle Based pH Sensor

In biological and environmental applications, pH is an important parameter that needs to be monitored at a regular basis. Conventionally, the measurement process takes a considerable amount of time involving several calibration steps and handling of fragile electrodes. In this work, we propose a new, robust and reliable way of sensing pH. The sensor has been fabricated based on tungsten oxide nanoparticle modified glassy carbon electrode (WO3/GCE) (Fig. 1). WO3 is a promising material for pH sensor because of its availability, stability, good morphological and structural control of the synthesized nanostructures, reversible change of conductivity, high sensitivity, selectivity and biocompatibility.1 Furthermore, WO3 is a well-studied wide band gap semiconductor (~2.75 eV) used for several applications as chromogenic material and catalyst.2 In this work, hydrothermal synthesis method was used for the fabrication of WO3 nanoparticles. For the fabrication of the pH sensor, the nanoparticles were mixed with Nafion and chitosan before drop coating onto the GCE surface. Scanning electron microscopy (SEM), x-ray diffraction (XRD), transmission electron microscopy (TEM) was used to characterize the nanoparticles. Cyclic voltammetry (CV) and square wave voltammetry (SWV) were used to monitor the potential shift based on different pH in the buffer solution. The WO3/GCE pH sensor showed a sensitivity of 1.15 VpH-1cm-2 at 25 °C and a potential drift of less than 5% after three hours of continuous use. The sensor showed good linearity at a pH range of 3 -10 and could retain 95% of its initial sensitivity after 1 week of use. The good sensitivity and long term stability of this WO3 based sensor may allow the development of a low cost pH sensor for a wider range of applications.3 Acknowledgement This work is financially supported by Science Foundation Ireland funded project “SweatSens” under the grant agreement No. 14/TIDA/2455 and the University Grant Commission (research support and publication division), Bangladesh. Corresponding authors' email addresses: mamun.jamal@chem.kuet.ac.bd and kafil.mahmood@tyndall.ie Reference 1. D. Vernardou, H. Drosos, E. Spanakis, E. Koudoumas, C. Savvakis, N. Katsarakis, J. Mater. Chem., 2011, 21, 513. 2. M. Natan, T. E. Mallouk, M. S. Wrighton, J. Phys. Chem. 1987, 91, 648. 3. L. Devlin, M. Jamal and K. M. Razeeb, Anal. Meth. 2013, 5, 880. Figure 1. Schematic diagram of WO3 nanoparticle based pH sensor. Figure 1

Development of a highly sensitive electrochemiluminescence sophoridine sensor using Ru(bpy)32+ integrated carbon quantum dots – polyvinyl alcohol composite film

A facile electrochemiluminescence (ECL) sensing platform for the sensitive analysis of sophoridine was constructed using Ru(bpy)32+/carbon quantum dots – polyvinyl alcohol composite film as modifier. The carbon quantum dots (CQDs) which have the ability to enhance the ECL intensity were synthesized through a simple hydrothermal method. As Ru(bpy)32+ was entrapped in the polyvinyl alcohol (PVA), it was beneficial to immobilize Ru(bpy)32+ efficiently on the GCE surface, and therefore a stable ECL signal could be obtained. In addition, the ECL response on the Ru(bpy)32+/CQDs/PVA composite system was greatly enhanced by sophoridine. Single-factor was applied to optimize the measurement conditions. The fabricated sophoridine sensor exhibited a well-proportional correlation between ECL intensity and the logarithm of sophoridine concentration in the range of 1.0×10−10–1.0×10−5M, and the detection limit was 5.0×10−11M (S/N=3). Moreover, the detection of sophoridine in blood serum was successfully accomplished and a desirable result by using the ECL sensing system was achieved, which indicated that the fabricated ECL sensor has potential value in sophoridine monitoring in practical samples.

The use of a signal amplification strategy for the fabrication of a TNT impedimetric nanoaptasensor based on electrodeposited NiONPs immobilized onto a GCE surface

This study reports on the evaluation of NiONPs layer as an efficient platform in designing a TNT nanoaptasensor. Based on this strategy, a film of electrodeposited NiONPs was immobilized onto the surface of a GCE. This film was used as a capture layer for the covalent attachment of Apt, which was a receptor element with regard to TNT. By incubating TNT onto the surface of the prepared Apt/NiONPs/GCE as a proposed nanoaptasensor, the Apt/TNT complex was formed and the changes of the electrochemical signal were evaluated with the EIS technique. The superior transduction platform and the Apts were densely populated at the surface of the modified electrode lowered the LOD, 33.5aM. Furthermore, the excellent antifouling ability of the NiONPs/GCE improves the operational stability and repeatability of the proposed nanoaptasensor. While most of the conventional approaches have used multistep chemical methods for modeling an apasensor, our proposed strategy provides the notable advantages the use of a single-step modification without employing any complex agent, the use of a simple procedure and not being time-consuming. The results indicated that the modification of a GCE with the electrodeposited NiONPs layer can expand the application of this strategy to develop some biosensors based on DNA in order to detect various targets.

Imprinted voltammetric streptomycin sensor based on a glassy carbon electrode modified with electropolymerized poly(pyrrole-3-carboxy acid) and electrochemically reduced graphene oxide

The authors describe a voltammetric sensor for trace analysis of streptomycin (STR). It is based on the use of a glassy carbon electrode that was modified with a film of STR-imprinted poly(pyrrole-3-carboxy acid) (PPy3C) on electrochemically reduced graphene oxide (ERGO). ERGO was first deposited on the surface of GCE by electro-reduction, this followed by deposition of a film of STR-imprinted PPy3C. The morphologies and properties of the sensor were characterized by scanning electron microscopy, cyclic voltammetry, and differential pulse voltammetry. Under optimized conditions, the sensor for STR displays two linear ranges that cover the 2 to 80, and the 80 to 1000 nM concentration range. Other features include a 0.5 nM limit of detection, good molecular recognition, and reliable practicability. Results indicate that the method provides a promising biomimetic platform for the determination of STR in food such as porcine kidney and honey.

Fabrication of highly sensitive gold nanourchins based electrochemical sensor for nanomolar determination of primaquine

A gold nanourchins modified glassy carbon electrode (AuNu/GCE) was developed for the determination of antimalarial drug, primaquine (PQ). The surface of AuNu/GCE was characterized by electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and cyclic voltammetry (CV). EIS results indicated that the electron transfer process at AuNu/GCE was faster as compared to the bare electrode. The SEM and TEM image confirmed the presence and uniform dispersion of gold nanourchins on the GCE surface. Upon investigating the electrochemical behavior of PQ at AuNu/GCE, the developed sensor was found to exhibit high electrocatalytic activity towards the oxidation of PQ. Under optimal experimental conditions, the sensor showed fast and sensitive current response to PQ over a linear concentration range of 0.01–1μM and 0.001–1μM with a detection limit of 3.5nM and 0.9nM using differential pulse voltammetry (DPV) and square wave voltammetry (SWV), respectively. The AuNu/GCE showed good selectivity, reproducibility and stability. Further, the developed sensor was successfully applied to determine the drug in human urine samples and pharmaceutical formulations demonstrating its analytical applicability in clinical analysis as well as quality control. The proposed method thus provides a promising alternative in routine sensing of PQ as well as promotes the application of gold nanourchins in electrochemical sensors.

PdCo porous nanostructures decorated on polypyrrole @ MWCNTs conductive nanocomposite—Modified glassy carbon electrode as a powerful catalyst for ethanol electrooxidation

In the current study, well-defined PdCo porous nanostructure (PdCo PNS) is prepared by a simple one-pot wet-chemical method and polypyrrole@multi-walled carbon nanotubes (PPy@MWCNTs) nanocomposite is used as a catalyst support. The morphology and the structural properties of the prepared catalyst were studied by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). The electrocatalytic performance of PdCo PNS/PPy@MWCNTs on glassy carbon electrode has been evaluated by cyclic voltammetry (CV), chronoamperometry (CA) and electrochemical impedance spectroscopy (EIS) techniques. The specific activity of PdCo PNS/PPy@MWCNTs for ethanol electrooxidation (1.65mAcm−2) is higher than those of other compared electrocatalysts. Also, PdCo PNS/PPy@MWCNTs catalyst represented higher electrocatalytic activity, better long-term stability and high level of poisoning tolerance to the carbonaceous oxidative intermediates for ethanol electrooxidation reaction in alkaline media. Furthermore, the presence of PPY@MWCNTs on the surface of GCE produce a high activity to electrocatalyst, which might be due to the easier charge transfer at polymer/carbon nanotubes interfaces, higher electrochemically accessible surface areas and electronic conductivity. The superior catalytic activity of PdCo PNS/PPy@MWCNTs suggests it to be as a promising electrocatalyst for future direct ethanol fuel cells.

Highly sensitive novel cathodic electrochemiluminescence of tris(2,2'-bipyridine)ruthenium(ii) using glutathione as a co-reactant.

Herein, glutathione was used as a co-reactant for the first time to generate a novel, highly stable, and enhanced cathodic electrochemiluminescence (ECL) on a simple bare glassy carbon electrode (GCE) surface using the Ru(bpy)32+ molecule in an alkaline pH phosphate buffer solution (PBS).

Novel N-Doped Carbon Dots/β-Cyclodextrin Nanocomposites for Enantioselective Recognition of Tryptophan Enantiomers.

Based on N-doped carbon dots/β-cyclodextrin nanocomposites modified glassy carbon electrodes (N-CDs/β-CD/GCE), an effective electrochemical sensor for enantioselective recognition of tryptophan (Trp) enantiomers was developed by differential pulse voltammograms (DPVs). Fluorescent N-CDs were synthesized through a hydrothermal method and characterized by spectroscopic approaches. The N-CDs/β-CD nanocomposites were efficiently electrodeposited on the surface of GCE through C–N bond formation between N-CDs and electrode. The obtained N-CDs/β-CD/GCE was characterized by multispectroscopic and electrochemical methods. Such N-CDs/β-CD/GCE generated a significantly lower Ip and more negative Ep in the presence of l-Trp in DPVs, which was used for the enantioselective recognition of Trp enantiomers. The N-CDs/β-CD nanocomposites showed different binding constants for tryptophan enantiomers, and they further selectively bonded with l-Trp to form inclusion complexes. This N-CDs/β-CD/GCE combined advantages of N-CDs with strong C–N binding ability and β-CD with specific recognition of Trp enantiomers to fabricate a novel sensing platform for enantioselective recognition of Trp enantiomers. This strategy provided the possibility of using a nanostructured sensor to discriminate the chiral molecules in bio-electroanalytical applications.

An environmental friendly electrode and extended cathodic potential window for anodic stripping voltammetry of zinc detection

This work reports on a novel polyeriochrome black T (poly(EBT) modified electrode for use as an environmentally-friendly electrode material that extends the cathodic potential window and improves the sensitivity and repeatability to detect zinc in industrial wastewater. The poly(EBT) film on the GCE surface was fabricated by electropolymerization. The surface morphology and electrochemical behavior of the modified electrode were characterized by scanning electron microscopy, fourier transform infrared spectroscopy and anodic stripping voltammetry. Under optimal conditions, the poly(EBT)/GCE exhibited a high hydrogen overvoltage (extended cathodic potential window). It provided a high sensitivity, a wide linear range (1.0 to 400.0μgL−1), a low detection limit (0.9μgL−1), had excellent repeatability and good recoveries (95% to 105%). This proposed modified electrode was applied to the determination of zinc in wastewater samples, and the results were consistent with those of an inductively coupled plasma atomic emission spectroscopy analysis.

Application of glassy carbon electrode modified with a carbon nanoparticle/melamine thin film for voltammetric determination of raloxifene

As a selective estrogen receptor modulator, raloxifene (RXF) prevent of osteoporosis in postmenopausal women by estrogenic actions on bone and decreases the risk of invasive breast cancer by anti-estrogenic actions on the breast and uterus tissue. However, RXF may increase the risk of blood clots, including deep vein thrombosis and pulmonary embolism. For the first time glassy carbon electrode modified with a thin film of melamine/carbon nanoparticles (CNPs/Mela) was constructed and used for the sensitive voltammetric determination of RXF. In comparison with unmodified electrode, the presence of the CNPs/Mela film resulted in a remarkable increase in the peak currents and sharpness of the waves, so that sub-micromolar concentrations of RXF became detectable. The surface morphology of the modified electrode, prepared by drop-casting of the CNPs/Mela suspension on the GCE surface, was characterized by scanning electron microscopy. The electrochemical response characteristics of the modified electrode toward RXF were studied by means of cyclic and differential pulse voltammetry. Experimental variables, such as the deposited amount of the modifier suspension, pH of the supporting electrolyte, the accumulation time and the potential scan rate were optimized by monitoring the electrochemical responses of RXF. Under the optimum conditions, the modified electrode showed a wide linear dynamic range of 0.04–2.0μM with a detection limit of 10.0nM for the voltammetric determination of RXF. The prepared modified electrode showed high sensitivity, stability and good reproducibility in response to RXF, confirming its usability for the accurate determination of trace amounts of RXF in pharmaceutical and clinical preparations.

Selective and Sensitive Nitrite Sensor Based on Glassy Carbon Electrode Modified by Silver Nanochains

AbstractHerein, we report a facile method for the synthesis of silver nanochains (Ag nanochains) using pyridine as growth directing agent and citrate ions as capping agents in alkaline medium. The characterization of the synthesized high aspect ratio Ag nanochains was accomplished with the help of Transmission Electron Microscopy (TEM) and High Resolution Transmission Electron Microscopy (HRTEM) which demonstrates the thickness below 100 nm. Crystalline nature of the synthesized Ag nanochains was investigated using X‐ray diffractrometry. A sensitive electrochemical nitrite sensor was assembled using synthesized Ag nanochains as electrode modifier. An improved cyclic voltammetric response for the oxidation of nitrite ions was witnessed at the modified GCE surface in comparison to bare GCE in Britton Robinson (BR) buffer (pH 4). The influence of pH on the oxidation peak current of nitrite ions was also examined using cyclic voltammetry. The electrocatalytic oxidation currents attained through amperometric measurements at Ag nanochains modified GCE were linearly dependent on the concentration of nitrite ions in the two ranges of 0.5–7.5 µM, 5–480 µM. Linear calibration plots of Ip vs. concentration of nitrite were also constructed at the proposed sensor using square wave voltammetry and differential pulse voltammetry. The proposed sensing strategy was successfully employed for the determination of nitrite in water samples with excellent recoveries.

A new strategy for simple and quick estimation of redox active nickel impurity in pristine SWCNT as nickel hexacyanoferrate by electrochemical technique

Residual metal impurities in the pristine carbon nanotubes (CNT) have been found to show an exceptional electrochemical and electro-catalytic properties. To quantify the impurities, sophisticated instrumental techniques and time consuming electrochemical methods have been adopted. Herein, we report, a new strategy for simple and quick detection of nickel impurity in pristine single walled carbon nanotube (SWCNT*Ni, *Ni=nickel impurity) as redox active nickel hexacyanoferrate hybrid (SWCNT*Ni-HCF) by potential cycling of the pristine SWCNT modified glassy carbon electrode (GCE/SWCNT*Ni) with ferricyanide in pH 2 KCl-HCl solution at a scan rate 50mVs−1 (t=12±1min). Quantitative stripping of the nickel as nickel ion that combines with ferricyanide to form Ni-HCF hybrid on the SWCNT surface (i.e., GCE/SWCNT*Ni-HCF) is found to be the mechanism for the observation. In-situ derivatization of NiO modified GCE with ferricyanide was studied as an important control experiment. A calibration plot was constructed by plotting surface excess value of GCE/Ni-HCF obtained by cyclic voltammetric experiment against NiO loading on unmodified GCE surface. Unknown concentration of nickel in the pristine SWCNT was then determined by substituting surface excess value of SWCNT*Ni-HCF in the calibration plot. Obtained value is comparable with the result of continuum source electro-thermal atomic absorption spectrometry method.

Electrocatalytic simultaneous determination of ascorbic acid, uric acid and l–Cysteine in real samples using quercetin silver nanoparticles–graphene nanosheets modified glassy carbon electrode

By immobilizing of quercetin at the surface of a glassy carbon electrode modified with silver nanoparticles and graphene nanosheets (Q–AgNPs–GNs–GCE) a new sensor has been fabricated. The cyclic voltammogram of Q–AgNPs–GNs–GCE shows a stable redox couple with surface confined characteristics. Q–AgNPs–GNs–GCE demonstrated a high catalytic activity for l–Cysteine (l–Cys) oxidation. Results indicated that l–Cys peak potential at Q–AgNPs–GNs–GCE shifted to less positive values compared to GNs–GCE or AgNPs–GCE. Also, the kinetic parameters such as the electron transfer coefficient,, and the heterogeneous electron transfer rate constant, k′, for the oxidation of l–Cys at the Q–AgNPs–GNs–GCE surface were estimated. In differential pulse voltammetric determination, the detection limit of l–Cys was obtained 0.28μM, and the calibration plots were linear within two ranges of 0.9–12.4μM and 12.4–538.5μM of l–Cys. Also, the proposed modified electrode is used for the simultaneous determinations of ascorbic acid (AA), uric acid (UA), and l–Cys. Finally, this study has demonstrated the practical analytical utility of the sensor for determination of AA in vitamin C tablet, l–Cys in a milk sample and UA in a human urine sample.

The selectivity of triethylene glycol modified glassy carbon electrode for charged and uncharged pieces

Abstract A triethylene glycol modified glassy carbon electrode (TEG–GCE) was fabricated by a controlled-potential electrolysis procedure. The performance of the film on the modified electrode surface was investigated by cyclic voltammetry with different probes. It was firstly found that while neutral pieces could penetrate the TEG film on the GCE surface, the ionic pieces, whatever it is anion or cation, was blocked by the film. This property was successfully used for determining dopamine (DA) in the presence of ascorbic acid (AA) with differential pulse voltammetry (DPV).

Voltammetric Determination of Folic Acid Using Adsorption of Methylene Blue onto Electrodeposited of Reduced Graphene Oxide Film Modified Glassy Carbon Electrode

AbstractThis work presents a sensitive voltammetric method for determination of folic acid by adsorbing methylene blue onto electrodeposited reduced graphene oxide film modified glassy carbon electrode (MB/ERGO/GCE) in 100 mM KCl‐10 mM sodium phosphate buffer solution (pH 7.40). The surface morphology of the MB/ERGO/GCE modified electrode was characterized using scanning electron microscopy, displays that both MB and ERGO distributed homogeneously on the surface of GCE. The MB/ERGO/GCE modified electrode shows more favorable electron transfer kinetics for potassium ferricyanide and potassium ferrocyanide probe molecules, which are important electroactive compounds, compared with bare GCE, MB/GCE, and ERGO/GCE. The electrochemical behaviors of folic acid at MB/ERGO/GCE were investigated by cyclic voltammetry, suggesting that the modified electrode exhibited excellent electrocatalytic activity towards folic acid compared with other electrodes. Under physiological condition, the MB/ERGO/GCE modified electrode showed a linear voltammetric response from 4.0 μM to 167 μM for folic acid, and with the detection limit of 0.5 μM (S/N=3). The stability, reproducibility and anti‐interference ability of the modified electrode were examined. The developed method has been successfully applied to determination of FA in tablets with a satisfactory recovery from 96 % to 100 %. The work demonstrated that the electroactive MB adsorbing onto graphene modified electrode showed an enhanced electron transfer property and a high resolution capacity to FA.

Square Wave Voltammetric Method for Simultaneous Determination of Bleaching Agents in Skin Cosmetics

Skin pigmentation disorders due to melanin excess, could have different causes. Kojic acid (KA) and hydroquinone (HQ) are depigmenting agents widely associated in pharmaceutical formulations to treat skin pigmentation disorders. An electroanalytical method was developed for simultaneous determination of these bleaching agents in skin whitening cosmetics. Cyclic voltammetry (CV) and square wave voltammetry (SWV) experiments were performed using a potentiostat/galvanostat µAutolab (Type III, Metrohm-Eco Chemie). A conventional three-electrode cell containing a glassy carbon (GCE) as working electrode (A=7,07 mm2), Pt disc (A=12,57 mm2) as counter electrode and Ag/AgCl (saturated aqueous KCl) as reference electrode were employed. Before use and between potential scans, the GCE surface was polished. Kojic acid exhibits a well-defined irreversible oxidation peak at 0.72V and hydroquinone a quasi-reversible redox peaks at 0.08 V and -0.02 V, characterized by adsorptive and diffusional processes, respectively. The influence of the pH was examined over the pH range from 2 until 8 in 0.04 mol L-1 Britton-Robinson buffer solution, the KA and HQ peaks potential shifts negatively with the increase of the pH value, due to the participation of protons in the oxidations processes. Others buffer solutions were examined at pH 8 and Mcllvaine was chosen to subsequent analytical purposes. The square wave voltammetric parameters were optimized by 23 Full Factorial Design including a central point assayed in quintuplicate. The statistical treatment of the data showed that the main effects and interaction effect of amplitude vs. frequency were significant at 95% confidence level. The best response is obtained at a= 40 mV, f= 40 s-1 and ΔES = 1mV. Under optimized conditions, the calibration curves were obtained in the concentration ranges of 3.5x10-5 to 2.5x10-4 mol L-1 (R= 0.9996) for kojic acid and 1.5x10-5 to 1.6x10-4 mol L-1 (R= 0.9994) for hydroquinone, with detection limits of 7.84x10-6 mol L-1 and 3.71x10-6 mol L-1 for KA and HQ, respectively. The proposed method was validated under parameters: specificity, linearity, range, limit of detection, limit of quantification, precision (repeatability and intermediate precision) and accuracy considering Brazilian Health Surveillance Agency (ANVISA) and International Conference on Harmonisation (ICH) guidelines. The developed and validated method has been successfully applied to the direct simultaneous determination of these compounds in real samples (gel and cream).

Electrochemical behavior of hydroquinone and catechol at glassy carbon electrode modified by electropolymerization of tetraruthenated oxovanadium porphyrin

This work presents the simultaneous determination of catechol (CC) and hydroquinone (HQ), employing a modified glassy carbon electrode with tetraruthenated oxovanadium (IV) porphyrin. The GCE was modified by electropolymerization of {VOTPyP[RuCl3(dppb)]4} porphyrin, onto the GCE surface, by cyclic voltammetry. The modified electrode, labeled as VOTPRu-GCE, showed two pairs of well-defined redox peaks for the electrochemical processes of catechol and hydroquinone. In bare GCE, the potential difference (ΔEp) of CC and HQ were 469mV and 457mV, respectively, while with VOTPRu-GCE the potential difference decreased to 29mV and 30mV, indicating that the redox processes were reversible onto the VOTPRu-GCE surface. With differential pulse voltammetry, it was possible to simultaneously determine the CC and HQ, with peak-to-peak potential separation of 129mV, in 0.1mol L−1 acetate buffer (pH 4.75). Under the optimized conditions, the calibration curves were obtained in the linear concentration ranges of 2–38μmolL−1 for both isomers using the VOTPRu-GCE, which showed high sensitivity in the determination of CC and HQ, 12.73 and 15.91μAμmolL−1cm−2, respectively. The detection limits were 0.41 and 0.55μmolL−1 for CC and HQ, respectively.