Modified Graphite Paste Electrode Research Articles

Selective Electrochemical Detection of Thymoquinone in Black Cumin Using Titanium Oxide-Modified Graphite Paste Electrode

Thymoquinone, a significant component in medicine and the spice industry due to its potent antioxidant properties, is the focus of this paper. The development of a titanium oxide-modified graphite paste electrode is presented for the detection of thymoquinone in black cumin. The electrochemical characteristics of the thymoquinone molecule were explored in a 0.1 M phosphate buffer solution of pH of 6. The modified graphite paste electrode exhibits excellent linearity across the concentration range of 0.1-200 [Formula: see text]M with limit of detection is 0.02 [Formula: see text]M. The developed electrode exhibits commendable repeatability, reproducibility and exceptional sensitivity towards thymoquinone. The separation of various concentrations of thymoquinone samples such as Mousumi, Priya Gold, Sunrise and DNV using Principal Component Analysis (PCA) with the Separability Index (SI) of 67.89 utilized to differentiate between different thymoquinone concentrations.

Application of a modified graphite paste electrode to the detection of fluorene in fuscous latices

A graphite paste electrode (GPE) was obtained by immobilizing graphene, and the electrocatalytic activity of fluorene (Flu) was studied. The voltammetric behavior using graphene-modified GPE showed an irreversible redox reaction for Flu-ACN-KClO4. A good linear correlation between anodic I and C Flu ranged within 8–300 ng mL−1. Therefore, we recommend a facile synthesis of modified GPE impregnated with Flu, which matched the concept of analytical minimalism. The electrochemical detection method combined with portable potentiostat is promising to be used for the field tests of Flu in fuscous latices as well as other polycyclic aromatic hydrocarbons.

Sensitive electrochemical determination of riboflavin at simple and low-cost poly (valine) modified graphite paste electrode

• A modest, responsive, low-cost, and green electrochemically polymerised valine modified graphite paste electrode was developed. • FE-SEM, EI, and CV measurements are used for electrode materials characterisation. • Riboflavin electrochemical redox action was analysed using polymerised valine modified graphite paste electrode. • prepared electrochemical sensor provides a lower limit of detection with fine sensitivity and reproducibility. • The modified electrochemical sensor gives acceptable recoveries for riboflavin in medicinal sample. A sensitive electrochemical analysis of riboflavin (RFN) was done in 0.1 M phosphate buffer solution (PTBS) by constructing a modest and green electrochemically polymerised (EP) valine (VLN) modified graphite paste electrode (GPE). The electrochemical, morphological, resistive, and conductive characteristics of modified electrode (EP(VLN)MGPE) and bare graphite paste electrode (BGPE) surfaces were clarified through cyclic voltammetry (CV), field emission scanning electron microscopy (FE-SEM), and Electrochemical impedance (EI) methods. The EP(VLN) initiated electrode surface parades excellent sensitivity, steadiness, repeatability, and reproducibility for the redox action of RFN with enhanced peak currents as associated to BGPE. The oxidation peak currents of RFN are improved with increased concentrations of RFN in the range from 2.0 µM to 40.0 µM and the attained limit of detection (LOD) and limit of quantification (LOQ) are found to be about 28.69×10 -8 M and 95.66×10 -8 M, respectively. The prepared EP(VLN)MGPE was beneficial for the quantitative and qualitative investigation of RFN in medicinal samples.

Selective Identification for Glucose in the Presence of Fructose Using Imprinted Polyeugenol Modified Graphite Paste Electrode

High blood glucose levels indicate diabetes mellitus. The conventional way was carried out to determine glucose levels, but this method just shows the total reducing sugar levels. An electrode was developed to analyze glucose in the presence of fructose by potentiometry. The optimum graphite paste electrodes-Imprinted based on polyeugenol and Ethylene Glycol Dimethacrylate (EGDMA) as crosslinkers, had been used as a glucose sensor. Polyeugenol was made by the polymerization reaction with a BF3 catalyst with a molecular weight of 6451.338 g/mol. A total of 2135.99 glucose was contacted with polyeugenol, and the result was crosslinked with EGDMA and 2,2'-Azobis(2-methylpropionitrile) (AIBN) initiator, then Molecularly Imprinted Polymer (MIP) was generated. The optimization of electrodes showed that the best composition of MIP: paraffin: graphite is 20:35:45 with the 19.16 mV/decade Nernstian Factor, which can measure samples at the range 10–5–10–1 M with a detection limit of 1.0334 × 10–5 M, a response time of 6–15 s, a lifetime (use) of 19 times and has good selectivity on fructose sample with Kij less than 1. Measurements using this electrode showed that honey contains 28.78% of glucose, not much different from the UV-Vis spectrophotometry, which is 29.68%, and HPLC is 30.42%.

Theoretical and electrochemical analysis of L-serine modified graphite paste electrode for dopamine sensing applications in real samples

In this study, we used the grinding modification approach to modify the carbon paste electrode (CPE) from an environmentally friendly catalyst (L-serine). L-serine(L-s) is shown to be an effective electrocatalytic at the modified CPE (MCPE) interface for detecting dopamine (DA). L-sMCPE showed excellent activity to detect DA in commercial injection samples with a recovery range of 98.9 to 100.5%. Theoretical studies were used to understand the electrocatalysis of L-serine at the atomic level using frontier molecular orbitals and analytical Fukui assay. The amine group of L-serine works as an extra oxidation site (cause for enhanced reduction peak DA) and a carboxylic acid group (reason for enhanced oxidation peak DA) at the L-sMCPE interface, according to our theoretical findings. Improvements to these processes might have a big influence on knowledge of the electrode interface for sensing applications.

Electrochemical behavior of hydroxychloroquine on natural phosphate and its determination in pharmaceuticals and biological media

The present work describes a simple, inexpensive and green electrochemical sensor based on natural phosphate modified graphite paste electrode (NPh–CPE) for the electrocatalytic determination of HCQ. The NPh–CPE has demonstrated a high performance toward HCQ electro-oxidation compared to unmodified carbon paste electrode in terms of oxidation current and potential. The HCQ electrochemical behavior at NPh–CPE was studied using cyclic voltammetry (CV), chronoamperometry (CA) and electrochemical impedance spectroscopy (EIS). Based on the investigation results, the electrode/analyte reaction characterization elucidates the ErCi mechanism as being a typical adsorption-controlled system. The response linearity, repeatability, accuracy and detection limit (LOD) were within the literature values range. The obtained detection limits were 5.27 × 10−7 mol L−1 and 3.34 × 10−7 mol L−1 for peak 1 and peak 2 respectively. The relative standard deviation (RSD) was found to be 2.8% for 5.0 × 10−6 mol L−1 of HCQ. The real samples analysis performed on human blood and pharmaceutical tablets have yielded satisfactory results.

A Simple Nano Cerium Oxide Modified Graphite Electrode for Electrochemical Detection of Formaldehyde in Mushroom

In this present work, electrochemical detection and quantification of formalin (FAL) trace present in mushroom (Agaricus bisporus) was premeditated using a cerium oxide nanoparticle modified graphite paste electrode (CeO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> @GP). Cerium oxide (CeO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) nanoparticles (nps) were synthesized through the sol-gel technique from cerium nitrate hexahydrate using poly (ethylene glycol) as a capping agent. The prepared CeO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> nps were characterized using X-ray diffraction (XRD) and transmission electron microscopy (TEM) techniques which revealed the successful formation of the cubic phase of CeO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> having crystallite size 4.84 nm. The prepared CeO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> nps were used to modify the graphite paste electrode (bare GP). Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) techniques were utilized to study comparative electroanalytical features of the fabricated electrodes. Under optimized experimental conditions, CeO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> @GP exhibited a wide linear range from 25 μM-1mM and a limit of detection of 1 μM. Moreover, CeO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> @GP featured high repeatability, reproducibility, and long-term stability. The electrode exhibited high selectivity for FAL in the presence of interferences like ethanol, methanol, formic acid, benzaldehyde, and acetone. CeO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> @GP demonstrated exceptional aptitudes in electrochemical behavior when subjected to mushroom extract.

An investigation of the mixed water/formamide solvent on the synthesis of cadmium nitroprusside particles and its behavior in the electrochemical sensing of isoniazid

Size-controlled cadmium nitroprussides, with particles in the micron meter or submicron size range (0.050–1.15 micron), (CdNPs) were prepared from total and varied compositions of water and formamide solvent in the complexation reaction of cadmium and nitroprusside ions. Four analytical systems (CdNP-1, CdNP-2, CdNP-3, and CdNP-4) were set up. The coordinated materials were investigated by spectroscopic and analytical techniques such as Raman spectroscopy, ultraviolet-visible spectroscopy (UV-Vis), X-ray diffraction (XRD), scanning electron microscopy (SEM), and cyclic voltammetry (CV). The CVs of the modified graphite paste electrode with CdNP-1, CdNP-2, CdNP-3, and CdNP-4 (10% m/m) exhibited a defined redox pair with formal potential (Eθ′) = 0.63 ± 0.02 V (ν = 20 mV s−1; KNO3 1.0 M). The dependence of particle size on the isoniazid electro-oxidation was verified by CdNP-3 and CdNP-4 microparticles.

Electrochemical Fabrication of Poly (niacin) Modified Graphite Paste Electrode and its Application for the Detection of Riboflavin

Objective:A poly niacin (NN) modified graphite paste electrode was prepared through a simple electrochemical polymerization route for the determination of Riboflavin (RF)Methods:Electropolymerization technique was used for the preparation of a modified electrode. The electrochemical impedance spectroscopy (EIS) method was used to study the surface behaviors and conductivity of the bare and modified electrodes. Cyclic voltammetry (CV) and linear sweep voltammetry (LSV) were used to study the electrochemical behavior of RF using 0.2 M PBS of 7.5 pH.Results:Poly niacin modified graphite paste electrode (PNNMGPE) provides more affinity towards RF detection with high sensitivity and selectivity over bare graphite paste electrode. RF calibration curve was obtained by LSV between 5.0 µM to 65.0 µM with 0.782 µM limit of detection (LOD) and 2.7608 µM limit of quantification (LOQ), respectively. Selective analysis of RF in the presence of ascorbic acid (AA) and dopamine (DA) was performed at PNNMGPE by the LSV method.Conclusion:The developed PNNMGPE was tested for RF analysis in a multivitamin tablet with good results. Furthermore, the developed electrode shows good stability and reproducibility.

Fabrication of Poly (Evans Blue) Modified Graphite Paste Electrode as an Electrochemical sensor for Sensitive and Instant Riboflavin Detection

Electro-analysis of Riboflavin (RN) consumed as vitamin has been delved by constructing the poly (Evans Blue) modified graphite paste electrode (PEBMGPE) as an electrochemical detector. Voltammetric determination of RN in 0.2 M PBS (pH 7.0) at the electro-active layer of the PEBMGPE was conducted. The PEBMGPE plays a crucial role as sensing tool towards the detection of RN compared to the BGPE. The topographical features of the bare graphite paste electrode (BGPE) and PEBMGPE was acquired by the FESEM surface analysis. All experimental factors such as applied potential, the effect of scan rate, impact of the pH were optimized. Employing the Differential pulse voltammetry (DPV) approaches using the good experimental circumstances the analytical curve was linear in the range of 6×10 -6 -1.5×10 -4 M, the detection limit and limit of quantification gained as 2.1×10 -7 M and 7.1×10-7 M, respectively. Subsequently, good repeatability, excellent reproducibility, and adequate stability, high sensitivity were achieved for the PEBMGPE sensor. In addition, the PEBMGPE sensor was applied for the interference study of RN with Dopamine (DA) and Paracetamol (PR). Besides the practicability of the projected sensor was successfully utilized for the detection of the RN in the pharmaceutical formulations

An Efficient Simultaneous Electrochemical Detection of Nanomolar Epinephrine and Uric Acid using Low Temperature Synthesized Nano‐sized Copper Telluride

AbstractHerein we developed a simple, cost effective, electrochemical sensor based on nanosized copper telluride (nps‐CuTe) for simultaneous detection of epinephrine (EP) and uric acid (UA). Voltammetric responses suggests dramatical improvement of electrocatalytic properties of both molecules by incorporating CuTe nps into unmodified graphite paste electrode (bare GP). Differential pulse voltammetric (DPV) measurement depicts large potential separation of 128 mV between EP and UA, allows their simultaneous determination from binary mixture. Under optimized condition, CuTe modified graphite paste electrode (CuTe/GP) manifested linear relationships of EP and UA in the range of 5–60 μM and 5–120 μM with detection limit (S/N=3) of 18 nM and 32 nM respectively. Moreover, CuTe/GP showed satisfactory response towards pharmaceutical and clinical samples for determining EP and UA concentrations.

Voltammetric Detection of Dihydroxybenzene Isomers By Modified Graphite Paste Electrode with Prussian Blue-Nanosized Polyaniline Hybrid

The dihydroxybenzene isomers (DHB); catechol (1, 2-dihydroxybenzene, CC), resorcinol (1, 3-dihydroxybenzene, RC) and hydroquinone (1,4-dihydroxybenzene, HQ) are well-known organic pollutants and are widely distributed in the environment. DHB isomers are frequently used as starting materials and industrial reagents in various industries for production of plastic, tanning, pharmaceuticals, paint, paper, cosmetics and rubber.1–4 Furthermore, these isomers are also found as important side products from the industrial effluents of photo-processing companies, oil refineries, coal-tar, steel, paper and pulp mills in concentrations ranging between 1 to 1000 ppm.4,5 Due to their toxicity and the health risks associated with their use, national environmental agencies from United States and European Union have categorized them as primary wastewater pollutants.6 In addition, Health Canada has also listed them under the List of Prohibited and Restricted Cosmetic Ingredients (Cosmetic Ingredient Hotlist).7 As an electroactive polymer, polyaniline (PANI) is known to have good environmental stability, conductivity and redox properties. It has also been recently used in electrochemical biosensors due to the ease of synthesis, cheap cost and simple doping mechanisms. Prussian blue (PB) is another redox substance which also possesses good conductivity and unique electrocatalytic characteristics. In this study, modified graphite paste electrode (GPE) with PB doped nanosized-PANI hybrid (PB@n-PANI/GPE) was used for simultaneous detection of DHB isomers using differential pulse voltammetry (DPV). Prussian blue doped nanosized-polyaniline (PB@n-PANI) was synthesized in two-steps, firstly, aniline and ferric (III) chloride salt reacted through in situ mechano-chemical reactions to produce nanosized-PANI polymer. Secondly, potassium hexacyanoferrate (II) solution was added to the product of step one and the polymer was doped by PB in a solid-state and template-free technique to generate PB@n-PANI. The synthesized hybrid was then characterized by different microscopic and spectroscopic techniques. The PB@n-PANI modified GPE exhibited three well-separated oxidation peaks at potentials 0.24, 0.36 and 0.74 V for HQ, CC and RC, respectively (Fig. 1). The analytical performance of the PB@n-PANI/GPE has been studied for simultaneous determination of HQ, CC and RS in different real sample matrices with satisfactory recoveries. Furthermore, different electrochemical techniques such as cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and chronoamperometry have been used to perform electrochemical surface characterization of the modified GPE. The results from CV and ESI were used to evaluate the charge transfer properties of the PB@n-PANI/GPE and the results from chronoamperometric studies were used to calculate the diffusion coefficients of the DHB isomers. In addition, active surface area of the modified GPE and the standard heterogenous rate constant for the DHB isomers have also been calculated. Overall, we have demonstrated that the presence of PB and n-PANI enhances the redox-active surface area and plays a synergistic role in improving the electrocatalytic activity of the PB@n-PANI/GPE. Therefore, PB@n-PANI/GPE is a promising analytical platform for simultaneous detection of DHB isomers.

Simultaneous and Individual Determination of Six Redox-Active Biomolecules Using a Modified Graphite Paste Electrode with Immobilized Ferric Cyanide-Chitosan Polymer Ion Pair on the Multi-Walled Carbon Nanotubes

Redox-active biomolecules such as Ascorbic acid (AA), Dopamine (DA), Uric acid (UA), Tryptophan (Trp), Xanthine (XA), and Caffeine (CA) are all critical for biological homeostatic maintenance. The depletion or over consumption in any of the biomolecules can lead to detrimental effects. For example, previous reports have suggested the depletion of dopamine in the brain is highly correlated to the progression of Parkinson’s disease 1. Caffeine, though not a bio-molecules, it is frequently consumed, and overdose can lead to neurological damage, or even death 2,3. In extension, these bio-molecules tend to exists as a mixture. Thus, it becomes important to develop a platform that enables the monitoring of these biomolecule concentrations simultaneously.In recent years, carbon nanotubes have collected a great amount of attention from the electrochemical sensor development communities 4. Due to their high surface to volume ratio, carbon nanotubes are able to enhance the electrical catalytic activity increasing the overall conductance 5. This characteristic is highly essential as not only it can increase the potential application range, it can also resolve and separate for biomolecules that have overlapping redox-potentials. In addition, nanotubes are highly biocompatible and do not pose a toxic effect on the biological system. In this work, a novel immobilized ferric cyanide-chitosan polymer ion pair on the multi-walled carbon nanotube-based nanocomposite was synthesized and utilized for the construction of a sensor platform capable of simultaneously detecting six redox-active biomolecules.Using Fourier-transform infrared spectroscopy, and scanning electron microscopy, the nanocomposite was shown to be successfully synthesized. Cyclic voltammetry, and electrochemical impedance spectroscopy both demonstrated the final modified electrode has improved electrochemical activity. Using differential pulse voltammetry, AA, DA, UA, Trp, XA, and CA were all detected simultaneously (Shown in Figure 1). Finally, the sensor performance was analyzed in real samples and demonstrated a comparable performance. These results demonstrated the reported sensor has a strong potential to become the next generation of biosensors. Reference 1. A. Nobili et al., Nat. Commun., 8, 14727 (2017).2. J. W. Daly, Cell. Mol. Life Sci., 64, 2153–2169 (2007).3. B. J. Gurley, S. C. Steelman, and S. L. Thomas, Clin. Ther., 37, 275–301 (2015).4. J. Wang, Electroanalysis, 17, 7–14 (2005).5. A. Eatemadi et al., Nanoscale Res. Lett., 9, 1–13 (2014). Figure 1

Surfactant Modified Graphite Paste Electrode as an Electrochemical Sensor for the Enhanced Voltammetric Detection of Estriol with Dopamine and Uric acid.

Purpose: Estriol (ERL) is a type of hormone among the groups of estrogen hormone that was detected through the voltammetric technique by constructing an electrochemical sensor based on the octoxynol-9 modified graphite paste electrode (OXL-9MGPE). Methods: Using the strategy of cyclic voltammetry (CV) and differential pulse voltammetry (DPV) with a bare graphite paste electrode (BGPE) immobilized with OXL-9, ERL electro-oxidation has been assessed in 0.2 M phosphate buffer solution (PBS) of pH 6.0. The fabricated electrode has substantial electrochemical sensing efficiency, and the ERL oxidation at the OXL-9MGPE was the irreversible process. The surface morphological characteristics of BGPE and OXL-9MGPE were differentiated with the help of field emission scanning electron microscopy (FE-SEM). Results: The impact of various factors such as scan rate, pH, reproducibility, repeatability, and stability on the electro-oxidation of ERL was evaluated. Techniques of CV and DPV were utilized to determine ERL, dopamine (DAN), and uric acid (URA) simultaneously with the projected sensor. The peak current was varied with ERL concentration in the range from 4×10-5 to 1.2×10-4 M at OXL-9MGPE. From this, the detection limit 1.4×10 -6 M and limit of quantification (LOQ) 4.7×10-6 M have been attained. Conclusion: As a result, OXL-9MGPE was successfully achieved as an electrochemical detector for the electro analysis of ERL via the CV technique.

Synthesis of a novel hybrid nanocomposite based on copper pentacyanonitrosylferrate and octa(aminopropyl)silsesquioxane and its behavior on l-cysteine electrooxidation

In this study, a novel silsesquioxane and copper pentacyanonitrosylferrate compound was prepared starting from octa(aminopropyl)silsesquioxane (CA) following a new synthesis route. The prepared composite (ACCuN) was characterized by spectroscopic techniques, such infrared (FTIR), Scanning Electron Microscopy coupled with Energy X-Ray (SEM-EDS), Transmission Electron Microscopy (TEM), X-ray Diffraction (XRD), Diffuse Reflectance UV/Vis, Electronic Paramagnetic Resonance (EPR) and cyclic voltammetry (CV). The cyclic voltammograms of the modified graphite paste electrode with ACCuN presented a redox pair with a formal potential of (Eθ') = 0.73 V (vs Ag/AgCl(sat.)) assigned to the redox couple Fe(II)(CN)5NO/Fe(III)(CN)5NO, respectively (vs Ag/AgCl(sat.); KCl 1.0 mol L−1; pH = 7.0; v = 20 mV s−1). The nanocomposite ACCuN was sensitive to l-cysteine concentrations, with a linear response from 2.0 × 10−4 to 2.0 × 10−3 mol L−1, relative standard deviation of ±2% (n = 3), and limit of detection and amperometric sensitivity of 1.25 × 10−4 mol L−1 and 10.66 mA/mol L−1, respectively.

A New Composite Based on Electroactive Zirconium Phosphate: Morfology, Structure and Their Behavior as a Voltammetric Sensor in the Ascorbic Acid Detection

An electroactive and chemically stable composite was obtained from zirconium (IV) isopropoxide (ZrI) and phosphoric acid (ZrP). The ZrP was characterized by techniques such as Fourier transform infrared spectroscopy, 13C and 31P nuclear magnetic resonance, X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy, thermogravimetric analysis, X-ray photoelectron spectroscopy, surface area and porosity and cyclic voltammetry. Voltammetric behaviour of the ZrP was obtained using of a modified graphite paste electrode in a potential range from − 0.20 to 1.00 V (vs Ag/AgCl). ZrP showed one redox couple with average potential $${E^{\theta ^{\prime}}}$$ = 0.30 V (vs Ag/AgCl(sat.)) (40% w/w; v = 20 mV s−1; KCl; 1.00 mol L−1). It was tested on electrocatalytic detection of ascorbic acid using cyclic voltammetry and square wave voltammetry. The modified electrode showed a detection limit of 2.4 × 10−5 mol L−1, with relative standard deviation of ± 3% (n = 3) and amperometric sensitivity of 11.7 mA/mol L−1 (R = 0.999) by using the cyclic voltammetry technique and a detection limit of 1.10 × 10−4 mol L−1 with relative standard deviation of ± 2% (n = 3) and amperometric sensitivity of 126.9 mA/mol L−1 (R = 0.998) by using the square wave voltammetry technique.

Ultra-trace determination of hexavalent chromium by novel two dimensional biphenol-biphenoquinone nanoribbons/silver nanoparticles

In this study, decorated silver nanoparticles on two dimensional (2D) -biphenol-biphenoquinone nanoribbons (AgNPs-BP-BPQ NRs) were prepared for the first time by a novel, fast and simple method. The mentioned compound was then used as modifier for preparation of modified graphite paste electrode (GPE/AgNPs-BP-BPQ NRs) for indirect voltammetric determination of carcinogen hexavalent chromium (Cr (VI). Peak current of BP/BPQ redox system was decreased in the presence of Cr (VI), hence, this decrease in peak current was used as the electroanalytical signal for quantitative determination of Cr (VI). Moreover, the redox reaction of Cr (VI) and BP was investigated in this study for the first time and the product was characterized. Different techniques such as field emission electron microscopy, Energy-dispersive X-ray spectroscopy, transmission electron microscopy, atomic force microscopy and fourier transform infrared spectroscopy were performed for characterization of the AgNPs-BP-BPQ NRs. Different electrochemical methods, such as cyclic voltammetry, electrochemical impedance spectroscopy and differential pulse voltammetry, were employed to study the behavior of Cr (VI) on the proposed modified electrode. Under the optimum conditions, the calibration curve was liner in the ranges of 8.0 × 10−11 to 1.0 × 10-8, 1.0 × 10-8 to 1.0 × 10-6 and 1.0 × 10-6 to 1.0 × 10-4 M with a detection limit of 2.0 × 10-12 M. Finally, this sensor was successfully used for determination of Cr (VI) in tap water, river water and electroplating waste water samples.

Reactivity of a Silsesquioxane Organofunctionalized with 4-Amino-5-Phenyl-4H-[1,2,4]-Triazole-3-thiol: Complementary Characterization and an Application to Chronoamperometric Detection of L-Dopamine

This work describes the organofunctionalization and a complementary characterization and application of an octakis(3-chloropropyl)octasilsesquioxane (1) with 4-Amino-5-Phenyl-4H-[1,2,4]-Triazole-3-Thiol (2). The functionalized silsesquioxane (3) was characterized by nuclear magnetic resonance, X-ray diffraction, transmission electron microscopy and thermogravimetric analysis. After functionalized, the silsesquioxane can interact with copper chloride and subsequently with potassium hexacyanoferrate (III) (4). The hybrid composite formed (4) was characterized by FT-IR and diffuse reflectance. The compound 4 included into a work graphite paste electrode (20% w/w) was examined for chronoamperometric determination of L-Dopamine. The modified graphite paste electrode with compound 4 showed a linear response from 2.5× 10− 5 at 4.0× 10− 4 mol L− 1. The modified graphite paste electrode with 4 showed a detection limit of 2.08× 10− 4 mol L− 1 with a relative standard deviation of ± 2% (n = 3) and amperometric sensitivity of 0.136 A mol L− 1.

Voltammetric Properties of Nickel Hexacyanoferrate (III) Obtained on the Titanium (IV) Silsesquioxane Occluded into the H-FAU Zeolite for Detection of Sulfite

A composite prepared from titanium (IV) silsesquioxane and phosphoric acid (TTiP) was prepared and occluded into the H-FAU zeolite (ZTTiP). The material was chemically modified with nickel and subsequently by potassium hexacyanoferrate (III) (ZTTiPNiH). It was preliminarily characterized by infrared spectroscopy (IR), energy dispersive X-ray spectroscopy (EDS) and cyclic voltammetry (CV). The voltammetric behavior of ZTTipNiH was obtained employing a modified graphite paste electrode (GPE) showing one well-defined redox couple with a formal potential of E $^{{\theta ^{\prime }}}=$ 0.51V (vs Ag/AgCl(sat)), KCl (3M) (20% w/w; v = 20 mV s− 1; KCl; 1.00 mol L− 1) corresponding to the NiIIFeII(CN)6/NiIIFeIII(CN)6 redox process. After rigorous voltammetric studies, the GPE modified with ZTTiPNiH was applied for facile and rapid detection of sulfite. From the analytical curve, a linear response was obtained in a concentration range of 0.05 to 0.80 mmol L− 1 and a detection limit (3σ) of 0.05 mmol L− 1 with a relative standard deviation of 4.21% (n = 3) and an amperometric sensitivity of 14.42 mA L mol− 1 for sulfite.

Enzyme immunoassay (ELISA/immunosensor) for a sensitive detection of pork adulteration in meat

ELISA/immunosensor were developed for a sensitive detection of pork adulteration in meat. Two formats of ELISA were performed. First, an extracted IgG was directly immobilized in the microplate. This assay allowed an identification of 0.01% as level of pork adulteration in 14 h15 min. In order to decrease the time of the assay, a competitive ELISA was developed by immobilizing IgG standard, which compete with the extracted IgG. This assay allowed a detection of 0.1% of pork adulteration in 45 min.Furthermore, two formats of electrochemical immunosensors were elaborated using the electro-entrapment of IgG in polymer modified graphite paste electrode. First, a direct immunosensor was capable of identifying 0.1 and 1% in raw and cooked meat respectively in 2 h. The second format was based on a competitive immunosensor, which was able to detect 0.01% of pork adulteration within 20 min.Both competitive immunoassays revealed high sensitivity, good specify and reduced analysis time.