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Bio-oils produced from three different biomass sources, namely cork, pinewood, and olive stones, are evaluated concerning their suitability and prospects of including their electrochemical transformations in a biorefinery scenario for the production of added-value compounds. Different types and concentrations of electrolytes (e.g., H2SO4, KOH) are added to the bio-oils to increase the samples' initially low ionic conductivity. The samples prepared by mixing bio-oil with 2 M KOH aqueous solution (50 vol.%) lead to a stable and homogeneous bio-oil alkaline emulsion suitable for electrochemical studies. The bio-oil samples are characterized by physicochemical methods (e.g., density, viscosity, conductivity), followed by analyzing their electrochemical behavior by voltammetric and chronoamperometric studies. The organics electrooxidation and the hydrogen evolution reaction in the bio-oils are assessed using Pt electrodes. Single- and two-compartment cell laboratory bio-oil electrolyzers are assembled using nickel plate electrodes. Electrolysis is carried out at 2.5 V for 24 h. Attenuated Total Reflection-Fourier-Transform Infrared Spectroscopy and Mass Spectrometry are applied to identify possible changes in the bio-oil samples' chemical structure during the electrolysis experiments. Comparing the analyses of the bio-oil samples subjected to electrolysis with the blank samples demonstrates that bulk electrolysis significantly changes the bio-oil composition. The bio-oil obtained from cork biomass shows the most promising results, but further studies are required to understand the nature of the actual changes. [ABSTRACT FROM AUTHOR]

The electrochemical detection and electrooxidation path of the first-generation antihistamine receptor hydroxyzine (HDZ) and its main metabolite cetirizine (CTZ) are addressed in this research. A carbon black-modified electrode to explore the electrochemical responsivity and electroanalytical detection of HDZ and CTZ was designed. Compared to the bare electrode, the irreversible anodic responses observed for HDZ and CTZ were considerably improved on the proposed carbon black-modified electrode, including twenty times enhancement of the anodic peak currents and the shifting of anodic peak potentials to less positive potentials. In order to identify the electrooxidation products resulting from the previously verified irreversible redox processes, cyclic voltammetric studies and potentiostatic electrolysis assays followed by products identification by nuclear magnetic resonance (NMR) spectroscopy were carried out. From the combination of electrochemistry and NMR spectroscopy data it was possible to propose electrooxidation reaction mechanisms for HDZ and CTZ molecules. By applying square-wave adsorptive anodic stripping voltammetry (SWAdASV) under optimized experimental conditions, the obtained analytical curves for HDZ and CTZ were linear from 2.99 × 10 − 7 to 9.81 × 10 − 6 mol L − 1 and from 4.97 × 10 − 7 to 1.08 × 10 − 5 mol L − 1 , with limits of detection of 1.00 × 10 − 7 mol L − 1 and 4.00 × 10 − 7 mol L − 1 , respectively. Finally, spiked synthetic human biological fluids were analysed by the proposed SWAdASV procedures, with recovery percentages close to 100%. [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]

A porous electrode material combining the features of vertically aligned multi-walled carbon nanotubes (VAMWCNT) and diamond-like carbon films (DLC) have been developed for a highly sensitive electrochemical sensor. For working electrode preparation, DLC has been grown onto VAMWCNT, forming a porous, conductive and stable composite. The electrochemical performance of this DLC:VAMWCNT electrode has been investigated toward detection and analysis of three well-known molecules, namely paracetamol, codeine and caffeine. A ternary mixture of these analytes was simultaneously determined under optimum experimental conditions using square-wave voltammetry. Wide linear concentration ranges and the limits of detection of 3.34×10−7 mol L−1, 1.57×10−7 mol L−1 and 3.67×10−7 mol L−1 were obtained for paracetamol, codeine and caffeine, respectively. We conclude that the proposed voltammetric method and the DLC:VAMWCNT electrode comprise a reliable methodology for simultaneous determination of paracetamol, codeine and caffeine in biological matrix samples. [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]

The electrochemical detection of two pharmaceuticals, propranolol (PROP) and hydrochlorothiazide (HTZ), was studied using a nitrogen-containing tetrahedral amorphous carbon (ta-C:N) electrode. Measurements were also made using a boron-doped diamond (BDD) electrode, for comparison. The ta-C:N electrode functioned well for the simultaneous determination of PROP and HTZ in artificial urine and serum by square-wave voltammetry, both of which were detected at high positive potentials. The PROP ( ca . 1.2 V) and HTZ ( ca. 1.4 V) oxidation peak potentials were separated by about 200 mV. The respective analytical response curves presented good linearity in the investigated concentration range from 0.9 to 9.8 μmol L −1 for PROP and from 3.0 to 9.8 μmol L −1 for HTZ with calculated limits of detection (S/N = 3) of 0.75 μmol L −1 (∼194 ng/mL) for PROP and 2.50 μmol L −1 (∼744 ng/mL) for HTZ. Essentially, the lowest concentration measured voltammetrically was the LOD. The results indicate that the ta-C:N electrode could be an excellent new carbon material for electrochemically-active analytes requiring high potentials for detection. [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]

A novel vertically aligned carbon nanotube/graphene oxide (VACNT-GO) electrode is proposed, and its ability to determine atorvastatin calcium (ATOR) in pharmaceutical and biological samples by differential pulse adsorptive stripping voltammetry (DPAdSV) is evaluated. VACNT films were prepared on a Ti substrate by a microwave plasma chemical vapour deposition method and then treated with oxygen plasma to produce the VACNT-GO electrode. The oxygen plasma treatment exfoliates the carbon nanotube tips exposing graphene foils and inserting oxygen functional groups, these effects improved the VACNT wettability (super-hydrophobic) which is crucial for its electrochemical application. The electrochemical behaviour of ATOR on the VACNT-GO electrode was studied by cyclic voltammetry, which showed that it underwent an irreversible oxidation process at a potential of +1.08 V in pHcond 2.0 (0.2 mol L−1 buffer phosphate solution). By applying DPAdSV under optimized experimental conditions the analytical curve was found to be linear in the ATOR concentration range of 90 to 3.81 × 103 nmol L−1 with a limit of detection of 9.4 nmol L−1. The proposed DPAdSV method was successfully applied in the determination of ATOR in pharmaceutical and biological samples, and the results were in close agreement with those obtained by a comparative spectrophotometric method at a confidence level of 95%. [ABSTRACT FROM AUTHOR]

Pb2+ ions are highly toxic to living beings because they tend to bioaccumulate in the body. For this reason, the development of simpler, low‐cost, and easy‐to‐operate techniques that can detect and quantify low concentrations of metal ions would help to identify contaminating media and improve public health. This work proposes a Pb2+ voltammetric sensor based on a carbon paste electrode modified with hydrothermal biochar (hydrochar, HC) obtained from malt bagasse waste (HC/CPE). The obtained hydrochar was characterized by zero‐charge point, FT‐IR, XRD and thermogravimetry. The differential pulse adsorptive anodic stripping voltammetry (DPAdASV) technique was used to perform the Pb2+ determination. After optimizing important parameters for detecting Pb2+ ions and the parameters of the voltammetric technique employed, a linear response range of 0.50 to 7.06 μmol L−1 with a limit of detection (LOD) and limit of quantification (LOQ) of 55.0 and 181.5 nmol L−1 were achieved, respectively. The developed voltammetric procedure was applied towards the Pb2+ determination at tap water and river water samples, with excellent recoveries (ranging of 91.19 to 109.22 %), proving that the HC‐based electrode has great potential for detecting Pb2+ ions. Hydrothermal carbonization allowed the biomass to be converted into functionalized hydrochar, eliminating the need for subsequent functionalization/activation steps for use as a Pb2+ adsorbing material on the electrodic surface. The proposed sensor also proved to be easy to assemble and environmentally friendly by using biomass waste as the carbon material. Thus, the proposed sensor adds to the literature the possibility of simple and easy detection of metal ions with a waste reuse bias. [ABSTRACT FROM AUTHOR]

Carbon nanomaterials thin films have been attracted considerable attention in the last years due to relative low cost and excellent electrical conductivity features. We report here on novel sensor architecture consisted of a glassy carbon surface modified with manioc starch and nanodiamonds nanoparticles. Structural and morphological properties of this thin film were investigated by Fourier-transform infrared spectroscopy, X-ray diffraction, scanning and transmission electron microscopies. By using square-wave voltammetry as electroanalytical tool, the widely used herbicide diquat (DQ) was determined in environmental samples. The modified electrode presented a linear response to DQ in the concentration range of 5.0 × 10−7 to 4.6 × 10−5 mol L−1 with a limit of detection of 1.1 × 10−7 mol L−1. This novel sensor proved to be efficient to determine if DQ is present in rivers and drinking water samples. Unlabelled Image • Films based on nanodiamonds confined in biodegradable manioc starch are reported. • Diquat herbicide is determined by square-wave voltammetry. • Sub-micromolar detection of diquat is achieved by exploring the novel nanodiamonds based sensor. • The developed nanostructured sensor is efficiently applied for diquat quantification in environmental samples. [ABSTRACT FROM AUTHOR]

Direct electrochemical sensing of biomolecules in samples with complex matrices such as human serum and blood is challenged by sensor surface biofouling resulting from the adsorption of concomitant macromolecules, particularly proteins. In this research, nanoporous gold (NPG) electrodes prepared from dealloying of a low-cost silver‑gold alloy are applied as antibiofouling electrodes for the simultaneous determination of ascorbic acid (AA) and uric acid (UA). From cyclic voltammetric assays, the antibiofouling features of the fabricated NPG were interrogated in the presence of biofouling agents, fibrinogen (FN) and bovine serum albumin (BSA) proteins using ascorbic acid and uric acid as the redox probes. It was shown that the porous surface of NPG ensured a stable signal for the redox probe even in the presence of proteins found in biological samples. The antibiofouling capability of NPG is credited to the biosieving effect of the morphology of the NPG, restricting the diffusion of large proteins into gold pores while permitting access of small electroactive molecules to efficiently exchange electrons. By applying differential pulse voltammetry (DPV) under optimum conditions, the AA and UA biomolecules were simultaneously determined with limits of detection of 63.0 and 9.0 μM, respectively. The DPV signals of AA and UA were stable on NPG in a biofouling environment and, the proposed NPG sensor was successfully applied for the simultaneous determination of AA and UA in the mimic human serum sample of fetal bovine serum (FBS). Unlabelled Image • Redox sensing of uric and ascorbic acid under biofouling conditions was achieved. • Nanoporous gold (NPG) out performs planar gold electrodes in biofouling conditions. • Uric acid and ascorbic acid can be simultaneously detected in a complex matrix. • Voltammetric signals of AA and UA were stable under biofouling conditions at NPG. [ABSTRACT FROM AUTHOR]

We explored the use of carbon black (CB), graphene oxide (GO), copper nanoparticles (CuNPs) and poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) as electrode materials for the simultaneous determination of isoproterenol, acetaminophen, folic acid, propranolol and caffeine. The designed nanostructured surface was widely characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), contact angle measurements and electrochemistry. From electrochemical characterization assays carried out towards the potassium ferricyanide redox probe, fast electron transfer kinetics and a considerably higher electroactive surface area were observed for the modified electrodic surface based on CB, GO, CuNPs and PEDOT:PSS film. Using square-wave voltammetry (SWV), well defined and resolved anodic peaks were detected for isoproterenol, acetaminophen, folic acid, propranolol and caffeine, with peak-to-peak potential separation not less than 170 mV. Then, the SWV technique was explored for the simultaneous determination of quinary mixtures of these analytes, resulting in analytical curves with linear ranges and limits of detection at micromolar concentration levels. The practical viability of the proposed voltammetric sensor was illustrated in the analysis of human body fluid samples. The proposed sensor showed good repeatability and a successful application using urine and serum matrices, with recoveries close to 100%. [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]

We report a solvothermal synthesis of ultrasmall platinum nanoparticles (USPtNPs) with an average size of 0.204 (± 0.008) nm using reline deep eutectic solvent (DES) as a stabilizing medium at a temperature of 80 ºC. SEM and EDS were used to morphologically characterize the USPtNPs. These revealed approximately spherical shapes with emission lines characteristic of platinum. DES was characterized by FT-IR and NMR, which indicated its formation through hydrogen bonds between the precursors. DSC was also used to characterize the precursors and the formed DES. Furthermore, an electrochemical sensor for determining riboflavin (RB) in commercial energy drinks and biological fluids was developed using the USPtNPs together with multiwalled carbon nanotubes (MWCNT). The USPtNPs-DES/MWCNT/GCE film was characterized by SEM, which demonstrated the characteristic tubular morphology of MWCNT. The RB voltammetric response was studied, and a significant enhanced on the current response was observed, especially due to the USPtNPs. This sensor displayed a linear response for RB in the range of 0.02–1.2µmol L−1, with a limit of detection of 1.8 nmol L−1. Besides detectability at nanomolar range, excellent performance was verified for repeatability and anti-interference features. The sensor based on extraordinary USPtNPs synthesized in DES in a simpler and environmentally friendly way was successfully applied to determine RB in different matrices. • First synthesis of USPtNPs using deep eutectic solvent as stabilizing medium. • USPtNPs with an average size of 0.208 nm obtained in a solvothermal synthesis. • First sensor based on USPtNPs and MWCNTs to detect RB in biological and food samples. [ABSTRACT FROM AUTHOR]