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Contributing to the development of sustainable electroanalytical chemistry, electrochemically reduced graphene oxide (ERGO) films obtained from residual graphite of discharged Zn-C batteries are proposed in this work. Graphite from the cathode of discarded Zn-C batteries was recovered and used in the synthesis of graphene oxide (GO) by the modified Hummer's method. The quality of the synthesized GO was verified using different characterization methods (FT-IR, XRD, SEM, and TEM). GO films were deposited on a glassy carbon electrode (GCE) by the drop coating method and then electrochemically reduced by cathodic potential scanning using cyclic voltammetry. The electrochemical features of the ERGO films were investigated using the ferricyanide redox probe, as well as paracetamol (PAR) and hydroquinone (HQ) molecules as model analytes. From the cyclic voltammetry assays, enhanced heterogeneous electron transfer rate constants (k0) were observed for all redox systems studied. In analytical terms, the ERGO-based electrode showed higher analytical sensitivity than the bare and GO-modified GCE. Using differential pulse voltammetry, wide linear response ranges and limits of detection of 0.14 μmol L−1 and 0.65 μmol L−1 were achieved for PAR and HQ, respectively. Furthermore, the proposed sensor was successfully applied to the determination of PAR and HQ in synthetic urine and tap water samples (recoveries close to 100%). The outstanding electrochemical and analytical properties of the proposed ERGO films are added to the very low cost of the raw material, being presented as a green-based alternative for the development of electrochemical (bio)sensors with unsophisticated resources. [ABSTRACT FROM AUTHOR]

This work reports the construction of screen‐printed electrode (SPE) modified with carbon black (CB) and magnetic Fe3O4 nanoparticles coated with molecularly imprinted polymer (mag@MIP) based on an alternative low‐cost approach. The proposed device was used for the sensitive and selective voltammetric determination of the antibiotic ciprofloxacin. The results obtained from cyclic voltammetry pointed to the improvement of the SPE response toward the irreversible oxidation of ciprofloxacin after the modification of the electrode surface with CB‐based film and the magnetic preconcentration of mag@MIP containing adsorbed ciprofloxacin molecules. Compared to the non‐molecularly imprinted sensor (mag@NIP), the presence of cavities selective for ciprofloxacin recognition in the mag@MIP nanoparticles accounted for the improvement in analytical signal of the molecularly imprinted sensor. The application of differential pulse voltammetry for ciprofloxacin determination yielded a linear response in the concentration range of 0.5 to 7.0 μmol L−1. The repeatability and interference tests results showed that the proposed electrochemical sensor has good measurement accuracy and selectivity. The proposed device was applied for the voltammetric determination of ciprofloxacin in river water and synthetic urine samples, where recovery rates close to 100 % were recorded for all the samples. The quantification data obtained from the application of the proposed voltammetric method were quite consistent with those of the HPLC reference method. [ABSTRACT FROM AUTHOR]

A porous diamond-like carbon film deposited on vertically aligned multi-walled carbon nanotubes (DLC:VAMWCNT) was evaluated as an electrode material in flow injection analysis (FIA) with amperometric detection. The redox behavior of hydroquinone (H 2 Q) was carried out as proof of concept. From cyclic voltammetry tests, H 2 Q gave a heterogeneous electron transfer rate constant (k 0) of 4.9 × 10−3 cm s−1, which is comparable or better than those obtained with conventional electrodes. For the H 2 Q determination with the FIA-amperometry system, optimizations were performed regarding the supporting electrolyte, applied potential and FIA parameters (flow rate and sample injection volume). Under optimal conditions, the amperometric response of the DLC:VAMWCNT electrode was linear in the H 2 Q concentration range from 1.0 × 10−6 to 1.0 × 10−4 mol L−1, with a limit of detection (LOD) of 7.7 × 10−7 mol L−1. Interestingly, the DLC:VAMWCNT electrode displayed a very stable response under hydrodynamic conditions, with no memory effect while retaining accuracy towards the analysis of commercial H 2 Q-based dermatological creams. From these findings, DLC:VAMWCNT appears to be an outstanding candidate for flow injection analysis systems coupled to electrochemical detection. [Display omitted] • Porous diamond-like carbon prepared on vertically aligned carbon nanotubes • Amperometric flow injection analysis with porous diamond-like carbon electrode • Porous-diamond like carbon electrodes display stable response under flow conditions. • Hydroquinone amperometric determination in cosmetic samples [ABSTRACT FROM AUTHOR]

A novel electrochemical method for determination of losartan using a glassy carbon electrode modified with carbon black nanoparticles immobilized within a crosslinked chitosan film is proposed. The electrochemical behavior of losartan was investigated using cyclic voltammetry, which presented an irreversible oxidation peak at a potential of + 1.28 V vs. Ag/AgCl (3.0 mol L−1 KCl). The electroactivity of losartan on the modified electrode was significantly improved in terms of peak potential and peak current intensity comparatively to bare working electrode. Using square-wave voltammetry technique under optimized conditions, the modified electrode showed a linear response in the concentration range of 4.97 to 47.6 μmol L−1 with a limit of detection of 0.479 μmol L−1. The developed electrochemical method was successfully applied for the determination of losartan in pharmaceutical formulation samples, with results consistent with those obtained by a comparative UV-Vis spectrophotometric method at 95% confidence level. In addition, losartan quantification was also achieved at synthetic biological fluid samples. [ABSTRACT FROM AUTHOR]

Carbon Black (CB) has acquired a prominent position as a carbon nanomaterial for the development of electrochemical sensors and biosensors due to its low price and extraordinary electrochemical and physical properties. These properties are highly dependent on the surface chemistry and thus, the effect of functionalization has been widely studied for different applications. Meanwhile, the influence of CB functionalization over its properties for electroanalytical applications is still being poorly explored. In this study, we describe the use of chemically functionalized CB Vulcan XC 72R for the development of sensitive electrochemical biosensors. The chemical pre-treatment increased the material wettability by raising the concentration of surface oxygenated functional groups verified from elemental analysis and FTIR measurements. In addition, it was observed an enhancement of almost 100-fold on the electron transfer rate constant ( k 0 ) related to unfunctionalized CB, confirming a remarkable improvement of the electrocatalytic properties. Finally, we constructed a Tyrosinase (Tyr) biosensor based on functionalized CB and dihexadecylphosphate (DHP) for the determination of catechol in water samples. The resulting device displayed an excellent stability with a limit of detection of 8.7 × 10 −8  mol L −1 and a sensitivity of 539 mA mol −1  L. Our results demonstrate that functionalized CB provides an excellent platform for biosensors development. [ABSTRACT FROM AUTHOR]

The determination of eugenol employing voltammetry of immobilized microdroplets (VIM) is reported in this work. The construction of the electrode was based on a glassy carbon substrate modified with carbon black nanoparticles and eugenol standard or clove oil sample within a dihexadecyl hydrogen phosphate (DHP) film. The different experimental parameters related to this proposed procedure, i.e., supporting electrolyte composition, pH, ionic strength, and square-wave voltammetry (SWV) parameters (amplitude, frequency, and step potential) were optimized. By doing that, the SWV measurements were performed on the following optimum experimental conditions: 0.2 mol L−1 phosphate buffer solution (pH 2.0), amplitude 90 mV, frequency 30 Hz, and step potential 5 mV. The analytical curve for eugenol was linear in the wide range from 0.03 to 26 μg (r = 0.999) with limits of detection (LOD) and quantification (LOQ) of 0.13 and 0.42 ng, respectively. Three commercial clove oil samples were successfully immobilized and analyzed using the proposed VIM procedure showing eugenol concentrations ranging from 14.0 to 68.3%. Comparing the results obtained by the proposed and comparative procedure (spectrophotometric), relative standard deviations (RSDs) lower than 5.0% were verified, demonstrating the concordance of the results obtained by both methods. [ABSTRACT FROM AUTHOR]

New aspects related to electrochemical performance of modified carbon paste electrodes (CPE) of high analytical performance are presented in this work. We studied whether the functionalisation of graphite powder with oxygenated functional groups (graphite oxide, GrO) could affect the electrochemical features of a classical CPE. By introducing oxygen termination over the graphite surface, a remarkable improvement in electrochemical performance was verified, including enhancement of analytical signals and charge transfer kinetics, as demonstrated from electrochemical characterisation assays conducted by cyclic voltammetry and electrochemical impedance spectroscopy towards the potassium hexa-cyanoferrate (II/III) probe. In addition, a positive effect was noted from the anchoring of Au nanoparticles on GrOPE. In analytical terms, two biologically relevant molecules were simultaneously determined using the proposed modified electrode based on GrO and AuNPs: epinephrine (EP) and uric acid (UA). Using differential pulse voltammetry (DPV), wide linear concentration ranges were founded for the analytical curves of EP and UA, and the limits of detection of 1.0×10−7 mol L−1 (EP) and 5.0×10−8 mol L−1 (UA) were predicted, respectively. The designed electrochemical sensor showed excellent precision of measurement and appropriate applicability for the analysis of biological fluids. [ABSTRACT FROM AUTHOR]

New progress in the application of voltammetry of immobilized microparticles (VIM) technique in electroanalytical chemistry is reported in this work through the determination of hydroquinone in dermatologic cream samples. The designed electrode was based on a glassy carbon electrode modified with a crosslinked chitosan film containing immobilized carbon black nanoparticles and hydroquinone standards or sample. The electrochemical features of immobilized hydroquinone were explored, which a fast electron transfer kinetic was verified from the perfect reversible redox behavior of this molecule. All the experimental conditions were optimized, including supporting electrolyte condition (composition, pH, and ionic strength) and technical parameters of differential pulse voltammetry (DPV). Under the optimized experimental conditions, the analytical curve was linear by a wide concentration range from 2.7 to 43 ng, with detection and quantification limits of 0.045 and 0.15 ng, respectively. Two commercial dermatologic cream samples were successfully immobilized and analyzed using the proposed VIM procedure, and the results were similar to those recorded by a spectrophotometric comparative procedure. Our set of results represents a unique and exciting advance in the scenario of electroanalytical chemistry for future applications. [ABSTRACT FROM AUTHOR]

New insights into the design of highly sensitive, carbon-based electrochemical sensors are presented in this work by exploring the interesting properties of graphene oxide (GO) and ionic liquids (ILs). An electrochemical sensor based on the carbon paste electrode (CPE) modified with GO and IL was developed for the sensitive detection of ofloxacin using square-wave adsorptive anodic stripping voltammetry (SWAdASV). GO sheets were obtained from the acid treatment of graphene and characterized by scanning and transmission electronic microscopy (SEM and TEM) and selected area electron diffraction (SAED), and the electrochemical behavior of the modified GO-IL/CPE was explored by electrochemical impedance spectroscopy studies. The CPE modification with GO and IL allowed an 8.2 fold increase in the analytical sensitivity for ofloxacin sensing compared to the unmodified CPE. Under the optimized experimental conditions using the SWAdASV technique, the GO-IL/CPE sensor provided an analytical curve for ofloxacin in the concentration range of 7.0×10 −9 to 7.0×10 −7 mol L −1 , with a sensitivity of 7.7×10 6 μA L mol −1 and limit of detection of 2.8×10 −10 mol L −1 (0.28 nmol L −1 ). The proposed sensor was successfully applied for the ofloxacin determination in human urine and ophthalmic samples, with recoveries near 100%. The results were similar those obtained by a spectrophotometric comparative method. [ABSTRACT FROM AUTHOR]

Carbon paste electrodes (CPE) were modified with nitrogen-doped carbon nanotubes (N-CNTs) synthesized at 750 °C (N-CNT 750) and 850 °C (N-CNT 850), carboxyl functionalized carbon nanotubes (MWCNT COOH), and pristine carbon nanotubes (MWCNT). Their electrochemical properties were investigated and compared towards a common redox probe, potassium ferricyanide (K 3 [Fe(CN) 6 ]). The electrochemical responses were probed using cyclic voltammetry, and the results unveiled that modification with carbon nanotubes enhanced anodic peak currents (I pa) for the electrodes CPE/MWCNT COOH , CPE/N-CNT 750 and CPE/N-CNT 850 (I pa , p < 0.05 in relation to pure CPE). In particular, CPE modified with N-CNTs synthesized at 850 °C (CPE/N-CNT 850) exhibited better electrochemical response, with lower peak-to-peak potential separation (ΔE p , p < 0.05 in relation to pure CPE). Complementary studies were conducted to investigate the electroactive area (A) and heterogeneous electron-transfer kinetics (k 0). CPE/N-CNT 850 (0.034 ± 0.005 cm2) and CPE/MWCNT COOH (0.057 ± 0.002 cm2) presented more satisfactory results for the anodic and cathodic electroactive area (A), respectively. Kinetic studies revealed a higher k 0 (1.03 × 10−3 cm.s−1) for the CPE/N-CNT 850 electrode. Differential pulse voltammetry was employed for the electrochemical detection of Acetaminophen (AC). The response was linear for an AC concentration range from 66.2 to 259.7 μmol L−1, with the lowest detection limit (LOD) of 0.37 μmol L−1 and the highest sensitivity of 0.244 ± 0.002 μA L μmol−1 for the respective electrodes CPE/N-CNT 850 and CPE/MWCNT COOH. The CPE/N-CNT 850 and CPE/MWCNT COOH electrodes show the best correlation of results, the presence of polar groups on the surface of MWCNT COOH and a higher amount of graphitic nitrogen bond of N-CNT 850 suggest that these CNTs are particularly promising for applications in electrochemical fields. [Display omitted] • CNTs synthesized in different conditions were employed as modifiers in carbon paste electrode. • CPE/N-CNT 850 and CPE/MWCNT COOH displayed more satisfactory results regarding the electroactive area using [Fe(CN) 6 ]3−/4−. • CPE/N-CNT 850 exposed a higher k 0 for the redox probe. • Electrodes modified with N-CNT 850 and MWCNT COOH exhibited improved sensing capabilities for acetaminophen determination. • MWCNT COOH with polar groups and N-CNT 850 with a higher amount of graphitic nitrogen bond could improve their electrochemical properties. [ABSTRACT FROM AUTHOR]

The analytical potential of a boron-doped diamond electrode (BDD) and square-wave voltammetry (SWV) for the determination of rosuvastatin calcium (ROS) was investigated. The voltammetric response of the ROS molecule was evaluated with a BDD electrode that was subjected to anodic (positive polarization, + 3.0 V for 5.0 s) or cathodic (negative polarization, − 3.0 V for 15.0 s) pretreatments. The target analyte showed an irreversible anodic process at ≈ 1.4 V (vs. Ag/AgCl (3.0 mol L − 1 KCl)) with an enhanced current response at a BDD electrode that was cathodically pretreated. Using the cathodically pretreated BDD electrode, other experimental conditions were optimized, including the supporting electrolyte and SWV parameters. Under optimized experimental conditions, the analytical curve was linear in the ROS concentration from 9.40 to 88.8 mg L − 1 (9.40 to 88.8 μmol L − 1 ), with a correlation coefficient of 0.998 and limit of detection of 1.04 mg L − 1 (1.04 μmol L − 1 ). The proposed method was successfully applied for ROS determination in pharmaceutical formulations and the electrochemically determined quantity of drug was in close agreement with the results obtained using a spectrophotometric method at the 95% confidence level. Additionally, biological fluid samples of urine and human serum were directly analyzed by the proposed voltammetric procedure, with excellent results of recovery. [ABSTRACT FROM AUTHOR]

In this work, an alternative voltammetric procedure for the determination of Pb(II) was developed using a carbon nanotube paste electrode modified with crosslinked chitosan with glutaraldehyde (GA-CTS-CNTPE). Square-wave adsorptive stripping voltammetry (SWAdSV) was used and the relevant experimental parameters were optimized. Under optimal experimental conditions, the voltammetric response was linear in the range of 9.90×10−8 to 2.00×10−6 molL−1 with a detection limit of 5.70×10−8 molL−1. The proposed voltammetric method showed good repeatability and low interference from other metallic species. It was successfully applied in the determination of Pb(II) in natural water samples and the results were in very close agreement with those obtained using a comparative method (inductively coupled plasma optical emission spectrometry (ICP-OES)). [ABSTRACT FROM AUTHOR]

A simple and highly selective electrochemical method was developed for the single or simultaneous determination of dopamine (DA) and epinephrine (EP) in human body fluids using a glassy carbon electrode modified with nickel oxide nanoparticles and carbon nanotubes within a dihexadecylphosphate film using square-wave voltammetry (SWV) or differential-pulse voltammetry (DPV). Using DPV with the proposed electrode, a separation of ca. 360 mV between the peak reduction potentials of DA and EP present in binary mixtures was obtained. The analytical curves for the simultaneous determination of dopamine and epinephrine showed an excellent linear response, ranging from 7.0 × 10−8 to 4.8 × 10−6 and 3.0 × 10−7 to 9.5 × 10−6 mol L−1 for DA and EP, respectively. The detection limits for the simultaneous determination of DA and EP were 5.0 × 10−8 mol L−1 and 8.2 × 10−8 mol L−1, respectively. The proposed method was successfully applied in the simultaneous determination of these analytes in human body fluid samples of cerebrospinal fluid, human serum and lung fluid. [ABSTRACT FROM AUTHOR]

The ionic liquid (IL) 1-butyl-3-methylimidazolium tetrafluoroborate and carbon black (CB) nanoparticles were incorporated within a crosslinked chitosan film over the surface of a glassy carbon electrode, and the obtained architecture explored to the sensitive voltammetric sensing of Allura red colorant in soft drinking powders. The different electrodic surfaces were morphologically and electrochemically characterized. From the modification of glassy carbon electrode with IL and CB, a significantly enhanced voltammetric response was achieved toward the Allura red irreversible oxidation reaction. The type and amount of IL employed in the electrode modification step as well as all the others experimental parameters affecting the sensor response by square-wave adsorptive anodic stripping voltammetry (SWAdASV) were systematically optimized. Under the optimum experimental conditions, the proposed SWAdASV procedure provided a linear analytical curve in the concentration range of 3.98 × 10−8 to 9.09 × 10−7 mol L−1 and a low limit of detection of 9.1 × 10−10 mol L−1 (0.91 nmol L−1). The proposed sensor presented good precision and no matrice effects as shown from repeatability tests, concomitant studies and addition/recovery assays. The developed SWAdASV procedure was applied successfully in the determination of Allura red content in commercial soft drink powder samples, and the results were in close agreement with those obtained using a comparative spectrophotometric method at a confidence level of 95%. Image 1 • Nanostructured sensor based on carbon black nanoparticles and ionic liquid. • Synergism of carbon black and ionic liquid as electrode modifiers. • Electrochemical sensing of allura red at nanomolar levels. • Food analysis by electroanalytical tools. [ABSTRACT FROM AUTHOR]

Abstract A glassy carbon electrode (GCE) modified with single-walled carbon nanohorns (SWCNH) and zein (ZE), a prolamin type-protein find in maize, for the differential pulse adsorptive cathodic stripping voltammetric determination of fenitrothion (FT) is proposed. The proposed film was characterized by scanning electron microscopy, cyclic voltammetry and electrochemical impedance spectroscopy. Regarding the electrochemical characterization, comparing the results obtained by cyclic voltammetry and electrochemical impedance spectroscopy, the modified electrode (SWCNH-ZE/GCE) showed an electroactive surface area 3 times higher and faster electron transfer kinetic than bare GCE. By using differential pulse adsorptive cathodic stripping voltammetry and SWCNH-ZE/GCE the analytical curve exhibited a linear response ranging of 9.9 × 10−7 to 1.2 × 10−5 mol L−1, with a limit of detection of 1.2 × 10−8 mol L−1. The proposed sensor was successfully applied for the determination of FT pesticide in natural water and orange juice samples. Moreover, the electrochemical sensor showed good repeatability and reproducibility arising from the excellent film stability, suggesting that the proposed architecture has broad potential for applications in sensing and biosensing. Graphical abstract Unlabelled Image Highlights • Zein is a protein that can be used for thin film preparation. • Single-walled carbon nanohorns were applied in electrochemical sensors. • A voltammetric sensor for fenitrothion determination is proposed. • Fenitrothion is successfully quantified in orange juice and water samples. [ABSTRACT FROM AUTHOR]

[Display omitted] • A theoretical analysis was presented to understand the distributed capacitance and resistance in supercapacitors in the time domain. • The porous electrode behavior was characterized by two different time constants. • The dynamics of the charge-storage process were verified to occur in different ways at low and long polarization times. • It was verified a connection between the outer and inner surface areas and the charge-storage mechanism in supercapacitors. This study reports the in-situ characterization of nanosized carbon-based electrodes to identify and quantify the distributed capacitance and resistances verified in the time domain during the charge-storage process in aqueous-based symmetric coin cells. A theoretical model was proposed to represent the electrochemical response considering the presence of the so-called 'inner'/internal and 'outer'/external surface regions. The derivative analysis of the galvanostatic findings revealed the presence of two distinct voltage plateaux that were ascribed to the progressive assessment of the 'outer' and 'inner' surface regions by the ionic species. For the first time, it was demonstrated a connection between the heterogeneous surface nature of carbon electrodes and the charge-storage process in supercapacitors where different charge-storage dynamics regarding the migration of the ionic species can be identified due to the progressive transfer of ions from the 'outer' to the 'inner' surface regions as a function of the polarization time. The synthesized carbon materials were ex-situ characterized by scanning electron microscopy, Raman, and X-ray photoelectron spectroscopies. Specifically, the surface-modified MWCNTs allowed us to focus on a fundamental approach for studying the overall capacitance characteristics of nanostructured carbon-based electrodes. Thus, the charge-storage mechanism in the time domain and the individual contribution of the pseudocapacitance in the frequency domain were studied to clarify the real electrochemical behavior exhibited by porous carbon-based electrode materials. [ABSTRACT FROM AUTHOR]

An electrochemical method for the determination of clindamycin using a glassy carbon electrode modified with graphene oxide and gold nanoparticles within a film of crosslinked chitosan with epichlorohydrin (AuNPs-GO-CTS-ECH/GCE) is proposed. The electrochemical behavior of clindamycin was studied using cyclic voltammetry, and square-wave voltammetry (SWV). Under the optimized working conditions using 0.1 mol L −1 phosphate buffer (pH 7.0) solution as the supporting electrolyte, at a potential of +0.8 V vs. Ag/AgCl (3.0 mol L −1 KCl), using the SWV technique with the proposed AuNPs-GO-CTS-ECH/GCE electrode, the analytical curve showed a wide linear concentration range from 9.5 × 10 −7 to 1.4 × 10 −4 mol L −1 , with a limit of detection of 2.9 × 10 −7 mol L −1 . The voltammetric method was successfully applied in the quantification of clindamycin in pharmaceutical formulations, as well as synthetic urine and river water samples, with results similar to those obtained by a comparative method (HPLC). [ABSTRACT FROM AUTHOR]

In this work, an electrochemical sensor based on vertically oriented carbon nanotubes (voMWCNT), electrically wired via connection upon a copper plate, for the detection of tadalafil (TD) is reported. The voMWCNT is easily prepared via microwave plasma reactor with no additional post-treatment. The voMWCNT was characterized by scanning and transmission electron microscopy in addition to electrochemical characterization with cyclic voltammetry. Once TD is of easy access and used in the treatment of erectile dysfunction and related diseases, the quality control of this drug is of high importance. Using linear sweep voltammetry, the detection of TD was found to be possible from 0.85 to 8.9 μmol L−1, with an R2 of 0.992 with a limit of detection found to correspond to 78 nmol L−1. The quantification of TD in different pharmaceutical drugs, as well as the device stability, indicates that the voMWCNT has potential for the routine sensing of TD. Unlabelled Image [ABSTRACT FROM AUTHOR]

A low-cost and disposable microcell was constructed with a screen-printed electrode for the non-enzymatic electrochemical determination of creatinine. The working electrode was modified with carbon black and maintained in contact with paper-adsorbed iron (III) ions. A small sample volume of 3 μL was required for the device operation. Then, iron (III) ions were complexed in the presence of creatinine in a chemical step, followed by an electrochemical reduction of non-complexed metallic ions in excess. Cyclic voltammetry and differential-pulse voltammetry experiments were employed for the electrochemical characterizations and analytical performance evaluation of the microcell. The working electrode modification with carbon black provided a significant increase of analytical signal. The sensor presented a linear response for creatinine concentrations ranging from 0.10 to 6.5 mmol L−1, with a limit of detection of 0.043 mmol L−1. Experiments for creatinine determination in real samples were successful performed through of standard recovery in urine. Image 1 • Creatinine was determinate by a non-enzymatic, low-cost, and disposable microcell. • A small urine sample volume of 3 μL was required for the operation of the device. • The working electrode modification with carbon black provided a significant increase of analytical signal. [ABSTRACT FROM AUTHOR]