Modified Carbon Paste Electrode Research Articles

Anatase titanium oxide nanoparticles and multi-walled carbon nanotubes-modified carbon paste electrode for simultaneous determination of avanafil and doxorubicin in plasma samples

Patients who receive anticancer drugs, might experience loss of sexual desire together with erectile dysfunction as one of cancer medications’ adverse effects. This might have a negative effect on their psychological functioning and quality of life and accordingly phosphodiesterase type 5 (PDE5) inhibitors as sex stimulants are used. One of the recently FDA-approved members of this class of drugs is avanafil (AVN) that is administered to assist in improving penile erection. Because of the seriousness of the cancer patient's health condition, it is mandatory to recognize the possible pharmacokinetic interactions in case of administering other drugs at the same time. Therefore, a sensitive sensor derived from carbon paste electrode (CPE) modified with anatase titanium dioxide nanoparticles (TiO2-NPs) and multi-walled carbon nanotubes (MWCNTs) was designed for the simultaneous determination of AVN and the anticancer drug doxorubicin (DOX) in spiked and real rabbit plasma samples. X-ray powder diffraction (XRD), Fourier transform infrared (FT-IR), and scanning electron microscopy (SEM) were employed to fully characterize the fabricated electrode. The modified electrode offers a considerable improvement in voltammetric sensitivity toward oxidation of AVN and DOX, compared to the bare electrode. A good separation was achieved between the oxidation peak potentials of AVN (1.4 V) and DOX (0.8 V). The effect of different voltammetric parameters on the peak separation and sensitivity for both drugs was studied to select the optimum experimental conditions. It was found that the optimum pH for the simultaneous determination of both drugs was obtained utilizing a Britton-Robinson buffer (BR) of pH 3.0. Furthermore, the electrochemical oxidation of AVN and DOX was evaluated with different modified carbon paste electrodes using cyclic voltammetry (CV) and square-wave adsorptive anodic stripping voltammetry (SWAdASV). The analytical curves for the quantitative simultaneous determination of AVN and DOX exhibited acceptable linearity within the concentration range from (0.10–6.0 μmol L−1 for AVN) and (5.0–35.0 μmol L−1 for DOX) in spiked rabbit plasma. Detection and quantitation limits were determined to be 0.035 and 0.10 μmol L−1 in the case of AVN and 1.3 and 4.0 μmol L−1 in the case of DOX, respectively. The method was effectively applied for the analysis of AVN in real rabbit plasma samples after the coadministration of DOX. Moreover, the proposed voltammetric method was useful as a therapeutic drug monitoring method to investigate the possible pharmacokinetic interactions between AVN and DOX in real rabbit plasma. An increase in the level of AVN in rabbit plasma was observed after administering DOX, and accordingly, the dose of AVN should be adjusted and monitored.

Synthesis and characterization of graphene oxide- Cu NPs-Fe-MOF nanocomposite and its application to simultaneous determination of Eskazina and Dopamine in real samples

• GO-Cu NPs-Fe-MOF nanocomposite as modifier was prepared via ultrasound process. • GO-Cu NPs-Fe-MOF nanocomposite was used to make a modified carbon paste electrode. • The fabricated sensor was used to detect of Eskazina and Dopamine in real samples. In this paper, a nanocomposite containing graphene oxide (GO), copper nanoparticles (Cu NPs) and iron based metal–organic framework (Fe-MOF) was successfully prepared with a simple method via ultrasound process. The synthesized GO-Cu NPs-Fe-MOF nanocomposite was characterized using FT-IR, Raman spectroscopy, XRD and FESEM, and used to fabricate a modified carbon paste electrode (CPE) for the determination of Eskazina (ESK) and simultaneous determination of ESK and Dopamine (DA) for the first time. The efficiency of the sensor toward electrocatalytic oxidation of ESK was evaluated using cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Using DPV technique, the calibration graph of ESK at the surface of modified electrode demonstrated the linear response over the range of 0.4 – 495.2 μM including two linear segments with a detection limit of 0.10 μM. Also, electrochemical sensing of both of the drugs was done at the GO-Cu NPs-Fe-MOF/CPE in acetate buffer solution (ABS; pH 6.0, 0.1 M). By DPV, the introduced electrode could separate DA and ESK signals as two strong well-defined voltammetric peaks. Eventually, the applicability and reliability of the introduced sensor was investigated for the determination of the drugs in pharmaceutical and biological samples satisfactorily.

Electrochemical detection of Methadone by use of poly-l- arginine/carbon nanotubes composite modified carbon paste electrode (P-L-Arg/CNTs/CPE) in human urine

Electrochemical detection of Methadone by use of poly-l- arginine/carbon nanotubes composite modified carbon paste electrode (P-L-Arg/CNTs/CPE) in human urine

Two fabricated carbon paste electrodes for novel potentiometric determination of probenecid in dosage form and human plasma

Solid contact ion selective electrodes are extensively utilized owing to their marvelous performance over traditional liquid contact ones. The main drawback of those solid contact electrodes is aqueous layer formation which affects their constancy. Herein and to overcome this common drawback, a carbon paste electrode containing poly(3,4-ethylenedioxythiophene) was constructed and used for determination of probenecid at variant pH values. This modification decreased the potential drift down to 0.8 mV/h and improved its stability over 30 days. A Nernstian slope of − 57.8 mV/decade associated with a linear range of 1.0 × 10−6–1.0 × 10−2 mol/L was obtained. The modified carbon paste electrode successfully detected up to 8.0 × 10−7 mol/L probenecid. Results of this modified carbon paste electrode were also compared to unmodified one.

Green synthesis of silver nanoparticles using Phoenix dactylifera seed extract and their electrochemical activity in Ornidazole reduction

Over the past few decades, nanotechnology evolved into a significant, interdisciplinary research field on a global scale. Due to their extraordinary physicochemical, optical, and biological qualities, noble metal nanoparticles like gold, silver, palladium, and platinum are widely used in a variety of industrial and pharmaceutical procedures. In this study, a quick, low-cost, and environmentally friendly approach was used to create GAgNPs. Without using hazardous chemical substances, GAgNPs were produced using Phoenix dactylifera seeds extract as a reducing and stabilizing agent. The synthesized GAgNPs were characterized by UV-Visble, X-ray diffraction, and scanning electron microscopy. The presence of GAgNPs confirmed by the appearance of peak at 420 nm employing UV-Vis method, also affirmed by X-ray diffraction pattern, and the calculated size was about 28.72 nm. The electrochemical activity of GAgNPs was investigated through the elaboration of carbon paste-based sensor for the determination of ornidazole. The GAgNPs modified carbon paste electrode displayed a linear concentration range from 1.0 × 10−3 mol L−1 to 5.0 × 10−5 mol L−1 with a detection limit and quantification limit of 3.8 × 10−6 mol L−1 and 1.2 × 10−5 mol L−1, respectively. The proposed sensor was used for ornidazole analysis in milk samples, providing satisfactory recoveries of 105.7% and 102.7% with RSD below 4%.

The Experimental Design Approach in Square‐Wave Voltammetric Determination of Tamoxifen by NiO‐CPE**

AbstractDue to the explosive global increase of various cancers, the need to introduce/develop novel catalysts/sensors for quantitative determination of cancer drugs is emphasized. Nickel oxide nanoparticles (NiO‐NPs) calcined at 200 °C were used as a modifier of carbon paste electrode (CPE) to quantify tamoxifen (TAM) in an aqueous solution. The square wave voltammetry (SqW) was used due to its high sensitivity. The modified NiO‐CPE showed an SqW anodic peak current with a peak potential of about 420 mV in the NaOH‐supporting electrolyte. This peak current was decreased when TAM analyte was added to the test solution. Thus, this reduced peak current (Δi) was used to quantify TAM in solution. The experimental design used the response surface methodology (RSM) approach to study the simultaneous interaction effects between the influencing variables. The optimized run was associated with a 10 % NiO ingredient in the CPE, 0.3 M NaOH, an amplitude of 200 mV, a step potential of 3 mV, and a frequency of 25 Hz. A proportional behavior was obtained between the mentioned Δi and TAM concentration in the range of 10–60 nM. The detection (LOD) and quantification (LOQ) limits were 1.81±0.35 and 6.05±0.24 nM, respectively. Interfering and recovery results confirmed the applicability of the proposed NiO‐CPE electrode for TAM determination in complex matrixes and the direct assay of the drug in human serum.

Highly Sensitive Enzyme‐free Sensor Based on a Carbon Paste Electrode Modified with Binary Zinc Oxide/Polyaniline Nanocomposites for Dopamine, Ascorbic Acid and Uric Acid Sensing

AbstractHybrid composites ZnO/PANI were facily synthesized by a sonication process at room temperature. This procedure is non‐expensive, time/energy saving and environmentally safe. The as‐prepared ZnO/PANI were characterized by FTIR, UV‐vis spectroscopies and SEM in order to investigate the structure and morphology of the studied composites. The samples were used to modify carbon paste electrode (CPE) in order to develop electrochemical biosensors (ZnO/PANI/CPE). The sensing properties of the nanoparticles were evaluated for dopamine, ascorbic acid and uric acid non‐enzymatic detection. The effect of percentage of polyaniline in the composites and the effect of calcination on the biosensor's response were also examined in the present study. It was revealed that the existence of PANI in ZnO/PANI/CPE largely enhanced the electroactive surface area and therefore the sensitivity for electrochemical sensing. A good electrochemical behavior was noted for ZnO/40 wt% PANI‐cal/CPE modified electrode toward DA, AA and UA oxidation. The electroactive surface area of the previously mentioned modified electrode (0.235 cm2) was two times higher than that of the bare electrode (0.117 cm2). The liner relationships between current intensities and concentrations were found to be 0.01–1.4 mM, 0.1–1.3 mM and 0.01–0.12 mM, with detection limit of 0.029 mM, 0.063 mM and 0.007 mM, for DA, AA and UA respectively. In the mixtures of ascorbic acid (AA), dopamine (DA) uric acid (UA) and glucose (Glu) the sensor showed high selectivity of DA with low interference of ascorbic acid by a current change of 14 %. The as‐prepared ZnO/PANI/CPE biosensor displayed a good reproducibility and stability.

Development of an ultrasensitive chemically modified carbon paste electrode for selective determination trace amount of sulfate ion

A recently synthesized Schiff base complex of nickel ion was examined to investigate its potential to act as an ion carrier in carbon paste matrix. The carbon paste electrode (CPE) modified with the Schiff base complex represents a Nernstian slope of 29.7 mV/decade for sulfate ion through a broad concentration range of 7.5 × 10-9 – 1.5 × 10-3 M and a trace detection limit of 5.0 × 10-9 M. The CPE displays suitable reproducibility, appropriate lifetime (more than two months), fast response time (4 s) and excellent anti-Hofmeister selectivity versus a vast diversity of other inorganic anions and biological species. The temperature dependence of sensor potential was tested in the temperature range of 5–45 °C (temperature coefficient = 0.5 mV/◦C). The CPE is appropriate for SO42- determination in real samples such as mineral water and blood serum samples. The CPE detection limit is much better than the prior reported potentiometric sensors for the sulfate ion.

Voltammetric determination of Molnupiravir used in treatment of the COVID-19 at magnetite nanoparticle modified carbon paste electrode

To reduce the progression of the viral process in patients infected with COVID-19, new treatments and drug active substances are needed. One of these drugs is Molnupiravir (MNP) which has a direct antiviral effect and has also proven to be highly effective in reducing the azopharyngeal SARS-CoV-2 infectious virus and viral RNA. Due to the importance and frequent use of this drug in the treatment of COVID-19, its accurate, quick, and cheap detection in pharmaceutical or biological samples is crucial. In this work, electrochemical behavior and sensitive voltammetric determination of MNP are described using a magnetite nanoparticle modified carbon paste electrode (Fe3O4@CPE) for the first time. Fe3O4 nanoparticles (NPs) were characterized by recording their transmission electron microscopy (TEM) images, energy dispersive X-ray (EDX), and X-ray diffraction (XRD) spectra. Cyclic voltammetric measurements showed that MNP was irreversibly oxidized at Fe3O4@CPE at 760 mV in pH 2.0 Britton Robinson buffer solution (BRBS). The peak current of MNP was increased approximately threefold at Fe3O4@CPE compared to bare CPE due to a good electrocatalytic efficiency of Fe3O4 NPs. According to differential pulse voltammetric studies, the fabricated electrode exhibited a linear range (LR) between 0.25 and 750 µM with sensitivity and limit of detection (LOD) of 4591.0 µA mM−1 cm−2 and 0.05 µM, respectively. On the other hand, although lower sensitivity (327.3 µA mM−1 cm−2) was obtained from CV compared to DPV, a wider linear calibration curve between 0.25 and 1500 µM was obtained in CV. Studies performed in tablet samples confirmed that the Fe3O4@CPE exhibits high applicability for selective and accurate voltammetric determination of MNP in real samples.

Green synthesis of CaO nanoparticles conjugated with l-Methionine polymer film to modify carbon paste electrode for the sensitive detection of levofloxacin antibiotic

This work is aimed to use eggshells waste as a cheap precursor for the green synthesis of CaO nanoparticles. The prepared nanoparticles were characterized using XRD, FTIR, and SEM then conjugated with l- Methionine polymer film to modify carbon paste electrode. The modified electrode was used for the first time for sensitive and selective detection of levofloxacin (LEV) electrochemically. The electrochemical investigations of LEV showed that the utilized modifiers enhanced the electrocatalytic efficiency of the fabricated sensor resulting in a noticeable increase in the oxidation peak current when compared to unmodified CPE. The newly electrochemical sensor displays a good performance for detecting LEV and values of 0.64 × 10−9 M and 2.13 × 10−9 M for LOD and LOQ were obtained respectively. From other hand the collected results indicated two linear ranges, from 7.00 × 10−9 –1.00 × 10−7 M and from 1.00 × 10−7 – 3.00 × 10−6 M. Additionally, the manufactured sensor offered satisfactory selectivity toward LEV in the presence of various interferences, good stability, and reproducible response. Additionally, the suggested method was applied to determine LVS in biological samples and pharmaceutical formulation with recoveries between 96.50 to 100.55%.

Synthesis and surface characterization of a chemically modified carbon paste electrode and its application in determination of Hg(II) ion in water, food and dental amalgam samples

The development of an easy and affordable method for its determination in various samples is of major interest because the globe is affected by the toxicity of the environment caused by the presence of heavy metals, particularly mercuric ions. For the potentiometric measurement of Hg(II) ions in various materials, an unique carbon paste electrode was created using 1,3-Bis[2-(N-morpholino)acetamidothiophenoxy]propane (BMATPP) as a modifier. With a reaction time of six seconds, the electrode had a Nernstian slope of 30.01 ± 0.52 mV decade-1 over the concentration range of 5 × 10-9-1 × 10-3 mol/L (SD of 5 replicates). It was discovered that the pH range for use was 2.2 to 4.5 and that it was thermally stable up to 60 °C. The selectivity of the suggested sensor towards the Hg(II) ion was investigated using the separate solution method (SSM) and fixed interference technique (FIM), and it demonstrated a satisfactory selectivity. The interaction between the target Hg(II) ions and modifier was demonstrated by scanning electron microscopy (SEM) in conjunction with energy dispersive X-ray (EDX) and infrared (IR). The modifier's contact angle value demonstrated its lipophilicity, which is consistent with its stability and long life. With excellent F-test and t-test values obtained, the Hg(II) ion modified sensor was successfully used for potentiometric analysis of several real samples.

Fabrication of ultra-sensitive carbon paste electrode with nanocomposite CdS modification for electroanalysis of rafoxanide in dosage form and biological fluids

Abstract An anthelmintic, rafoxanide (RF), is frequently used in veterinary medicine to cure fascioliasis in cattle and sheep. A sensitive, quick, and selective detection of RF in its pharmaceutical preparation and in human urine was achieved through developing a new electrochemical sensor. The suggested method relied on the electro-oxidation of RF that used a modified carbon paste electrode in the presence of sodium dodecyl sulfate, which acts as an anionic surfactant. Voltammetric types were utilized in RF analysis, and these methods were cyclic voltammetry and differential pulse techniques. The suggested electro-analytical method’s validity is verified using the International Council on Harmonization (ICH/Q2) rules. The calibration curve for RF quantification was done in the concentration range from 2.9 × 10−6 to 3.1 × 10−4 M at cadmium sulfide modified carbon paste electrode. The limit of detection and the limit of quantification LOQ were found to be 6.7 × 10−7 M and 2.01 × 10−6 M, respectively. This study could be applied to the examined drug in QC-laboratory units, and also RF could be assayed in its pharmacokinetic studies.

Powerful and fast nanostructure electrochemical sensor for monitoring of carbidopa catechol-based drug in water and biological fluids

Herein, to monitor the concentration of carbidopa in an aqueous solution, an analytical approach based on electrode surface modification by Pt/SWCNTs as a sensor has been proposed. Pt/SWCNTs was synthesized by polyol strategy and characterized by the TEM method. Results confirmed spherical Pt nanoparticles with a diameter of about 10 nm decorated at the surface of SWCNTs with good distribution. The carbon paste electrode modified (CPEM) with Pt/SWCNTs was fabricated by mixing 12% of nanocomposite as an optimum condition with graphite powder in the presence of paraffin oil as a binder. Carbidopa's oxidation signal was enhanced by about 2.73 times when using the CPEM/Pt/SWCNTs, and its oxidation potential was decreased by about 110 mV. Additionally, the sensor demonstrated a linear dynamic range of 1.0 nM–120 M with a detection limit of 0.5 nM at pH = 7.0 as the ideal condition for monitoring carbidopa. Therefore, carbidopa in water and dextrose saline can be detected using CPEM/Pt/SWCNTs with an acceptable recovery range.

Advanced experimental techniques for the sensitive detection of a toxic bisphenol A using UiO-66-NDC/GO-based electrochemical sensor

In the present study, a simple and sensitive method for detecting bisphenol A (BPA) in various environments, including groundwater, was described using a widespread electrochemical method. BPA is well-known for its endocrine-disrupting properties, which may cause potential toxicological effects oon the nervous, reproductive, and immune systems. A novel metal-organic framework (UiO-66-NDC/GO) was synthesized, and its existence was confirmed by several characterization techniques like FTIR, UV–visible, XRD, SEM-EDX, Raman spectroscopy, and TGA. Due to the excellent electrocatalytic nature, UiO-66-NDC/GO was chosen as the sensor material and integrated on the surface of the bare carbon paste electrode (BCPE). The UiO-66-NDC/GO modified carbon paste electrode (MCPE) was engaged for the detection of BPA using techniques like cyclic Voltammetry (CV), differential pulse voltammetry (DPV), and electrochemical impedance spectroscopy (EIS). The applied sensor exhibited an astonishing outcome for BPA detection with high sensitivity and selectivity. The lower detection limit (LLOD) of 0.025 μM was achieved at the modified sensor with a linear concentration range of 10–70 μM. Moreover, the practical applicability of the sensor was tested on tap water, drinking water, and fresh liquid milk, giving an excellent recovery of BPA in the range of 94.8–99.3 (v.%). The proposed method could be employed for electrochemical device or a solid state device fabrication for the onsite monitoring of BPA.

Electrochemical sensing of the maple syrup urine disease biomarker valine, using saffron-silver nanoparticles

Metabolic disorders are inherited disorders in which genetic defects prevent a metabolic pathway and cause enzymes to malfunction. Maple syrup urine disease (MSUD) is a rare metabolic disease marked by high levels of branched-chain amino acids (b-AAs), leucine, isoleucine, and valine. Elevated concentrations of b-AAs pose issues including liver failure, neurocognitive impairment, and mortality. Given the unavoidable repercussions for newborns, it is critical to establish quick and adaptable diagnoses in the early stages of life. Thus, this study highlights the development of a novel electrochemical sensor for valine detection (MSDU biomarker) based on a modified carbon paste electrode (CPE) with electropolymerized silver nanoparticles capped with saffron (AgNPs@Sa) synthesized using a green method. Thus, a modified carbon paste electrode (CPE) with a conductive polymer posing silver nanoparticles was employed to sensitively determine Val in this paper. Saffron capped with silver nanoparticles (AgNPs@Sa) were synthesized, using a green method and studied using cyclic and square wave voltammetry. Cyclic voltammetry (CV) was used in the electropolymerization of AgNPs@Sa on CPE (poly-AgNPs@Sa-CPE) and utilized in the detection of Val. The modified electrode under the selected conditions produced square wave signals with valine mass concentrations ranging from 0.258 to 11.94 ng L−1 in the case of buffer solutions and it was successfully applied in urine samples. The assay proved to be simple, rapid, and cost-effective, sensitive with a low detection limit of 0.085 and 0.097 ng L−1 for buffer and urine samples, respectively.

Synthesis and Characterization of High Entropy Alloy 23Fe-21Cr-18Ni-20Ti-18Mn for Electrochemical Sensor Applications.

High entropy alloys (HEA) are one of the modern-era alloys accelerating with greater velocity because of their excellent properties and different applications. In the present paper, we have successfully fabricated HEA (23Fe-21Cr-18Ni-20Ti-18Mn) powders by ball milling the elemental Fe, Cr, Ni, Ti, and Mn powders for 15 h. The advancement of the milling process and phase transformation of HEAs were studied by using X-ray diffraction (XRD) and scanning electron microscope (SEM). The crystallite size and the lattice strain of the HEA were calculated by using the Williamson-Hall (W-H) equation and the values were found to be 7 nm and 0.0176%, respectively. Similarly, the true lattice parameter was calculated using the Nelson-Riley (N-R) extrapolation method, and the value was found to be 3.544 Å. We have successfully investigated the electrochemical response of 15 h ball milled 23Fe-21Cr-18Ni-20Ti-18Mn HEA powders to determine the ascorbic acid (AA) using cyclic voltammetry. We have modified the carbon paste electrode with ball milled HEA of concentrations 0, 2, 4, 6, 8, and 10 mg, and among them, 8 mg HEA modified carbon paste electrode (HEA-MCPE) depicted the highest current sensitivity. We reported the effect of modifier concentration, analyte concentration, scan rate, and pH on the oxidation peak of AA. The electrochemical active surface area of carbon paste and MCPE was calculated using the Nernst equation and the values were found to be 0.0014 cm2 and 0.0027 cm2, respectively. The fabricated HEA-MCPE showed excellent current sensitivity, stability, anti-fouling, and selectivity.

Electrochemical Determination of Morphine in Urine Samples by Tailoring FeWO4/CPE Sensor.

Morphine (MORPH) is natural alkaloid and mainly used as a pain reliever. Its monitoring in human body fluids is crucial for modern medicine. In this paper, we have developed an electrochemical sensor for submicromolar detection of MORPH. The sensor is based on modified carbon paste electrode (CPE) by investigating the FexW1-xO4 ratio in iron tungstate (FeWO4), as well as the ratio of this material in CPE. For the first time, the effect of the iron-tungsten ratio in terms of achieving the best possible electrochemical characteristics for the detection of an important molecule for humans was examined. Morphological and electrochemical characteristics of materials were studied. The best results were obtained using Fe1W3 and 7.5% of modifier in CPE. For MORPH detection, square wave voltammetry (SWV) was optimized. Under the optimized conditions, Fe1W3@CPE resulted in limit of detection (LOD) of the method of 0.58 µM and limit of quantification (LOQ) of 1.94 µM. The linear operating range between 5 and 85 µM of MORPH in the Britton-Robinson buffer solution (BRBS) at pH 8 as supporting electrolyte was obtained. The Fe1W3@CPE sensor resulted in good selectivity and excellent repeatability with relative standard deviation (RSD) and was applied in real-world samples of human urine. Application for direct MORPH detection, without tedious sample pretreatment procedures, suggests that developed electrochemical sensor has appeared to be a suitable competitor for efficient, precise, and accurate monitoring of the MORPH in biological fluids.

Simultaneous Determination of Dopamine and Uric Acid in Real Samples Using a Voltammetric Nanosensor Based on Co-MOF, Graphene Oxide, and 1-Methyl-3-butylimidazolium Bromide.

A chemically modified carbon paste electrode, based on a CoMOF-graphene oxide (GO) and an ionic liquid of 1-methyl-3-butylimidazolium bromide (CoMOF-GO/1-M,3-BB/CPE), was fabricated for the simultaneous determination of dopamine (DA) and uric acid (UA). The prepared CoMOF/GO nanocomposite was characterized by field emission-scanning electron microscopy (FE-SEM), the X-ray diffraction (XRD) method, a N2 adsorption-desorption isotherm, and an energy dispersive spectrometer (EDS). The electrochemical sensor clearly illustrated catalytic activity towards the redox reaction of dopamine (DA), which can be authenticated by comparing the increased oxidation peak current with the bare carbon paste electrode. The CoMOF-GO/1-M,3-BB/CPE exhibits a wide linear response for DA in the concentration range of 0.1 to 300.0 µM, with a detection limit of 0.04 µM. The oxidation peaks' potential for DA and uric acid (UA) were separated well in the mixture containing the two compounds. This study demonstrated a simple and effective method for detecting DA and UA in real samples.

Regenerable sensor based on tris(4,7′-diphenyl-1,10-phenanthroline)ruthenium (II) for anodic and cathodic electrochemiluminescence applications

Tris(4,7′-diphenyl-1,10-phenanthroline) ruthenium (II) dichloride [Ru(dpp)32+] was used for the first time to construct a regenerable electrochemiluminescence (ECL) sensor. The Ru(dpp)32+-modified carbon paste electrode (CPE) showed several unique features in comparison with commonly studied Ru(bpy)32+-modified electrodes. On the one hand, a quite reversible reduction peak was observed at −0.96 V where no obvious hydrogen evolution occured, enabling the sensitive detection of S2O82−. Moreover, our proposed S2O82− sensor showed a good linear range from 3 × 10−9 to 3 × 10−4 M with a detection limit of 2 nM, indicating higher sensitivity for the same analyte than previously reported ECL methods by about two orders of magnitude. On the other hand, the Ru(dpp)32+-modified electrode showed an irreversible oxidation peak because electrogenerated Ru(dpp)33+ is very reactive in aqueous solutions, while Ru(bpy)32+-modified electrode showed a reversible oxidation peak. Moreover, the present sensor showed a good linear range from 10−7 M to 10−3 M for oxalate with a detection limit of 60 nM. It detected oxalate in urine samples with nice recoveries. The regenerable ECL sensor presented good characteristics, such as low cost, simple fabrication procedure and fast response time. The Ru(dpp)32+ based regenerable sensor is an attractive alternative to Ru(bpy)32+-based regenerable sensor, as it can be used for both anodic and cathodic ECL analysis with high sensitivity in aqueous media.

Development of an electrochemical sensor based on Ce3+ and CuO for the determination of amaranth in soft drinks

A novel Ce3+-doped CuO nanocomposite was synthesized in the present study. The proposed modified carbon paste electrode (Ce3+-doped CuO/CPE) was applied to detect amaranth. Cyclic voltammetry and differential pulse voltammetry were employed to evaluate the electrochemical responses of modified electrode. The oxidation signal of Ce3+-doped CuO/CPE in the presence of amaranth was enhanced which could be related to the synergistic effect of cerium and CuO that improved the electrochemical behavior of electrode for oxidation of amaranth. In this study, the surface areas of bare, CuO/CPE and Ce3+-doped CuO/CPE were calculated 0.043, 0.131 and 0.147 cm2, respectively. The presence of Ce3+-doped CuO at the electrode surface, effectively increased electron transfer rate and surface area which improved the sensitivity of electrode for amaranth determination. Using the scan rate, a diffusion-controlled electrochemical process for the amaranth oxidation on Ce3+-doped CuO/CPE was confirmed. The diffusion coefficient of 1.37×10−5 cm2 s−1 for amaranth was calculated based on the chronoamperometry analysis. The response was linearly for amaranth in the range between 0.05 and 240.0 μM and the limit of detection and limit of quantification were calculated to be 10.2 and 30.9 nM, respectively. Based on the results, the present electrode showed suitable stability, reproducibility and repeatability for amaranth detection. In addition, the proposed electrode was employed to detect amaranth in real specimens, the results of which showed successful outputs.