[en] Second order supersymmetry transformations which involve a pair of complex conjugate factorization energies and lead to real nonsingular potentials are analyzed. The generation of complex potentials with real spectra is also studied. The theory is applied to the free particle, one-soliton well and one-dimensional harmonic oscillator

[en] It is shown that the radial part of the hydrogen Hamiltonian factorizes as the product of two not mutually adjoint first-order differential operators plus a complex constant ε. The 1-SUSY approach is used to construct non-Hermitian operators with hydrogen spectra. Other non-Hermitian Hamiltonians are shown to admit an extra 'complex energy' at ε. New self-adjoint hydrogen-like Hamiltonians are also derived by using a 2-SUSY transformation with complex conjugate pairs ε, ε-bar

[en] Graphical abstract: Display Omitted - Highlights: • Anodic stripping voltammetry of Zn at gold electrode for fuel bioethanol analysis. • Portable batch injection analysis coupled to anodic stripping voltammetry. • Efficient gold electrode cleaning between measurements of Zn in fuel bioethanol. • Adequate sensitivity, recovery values and no sample treatment required. • On-site determination of metals on fuel bioethanol using mercury-free electrode. - Abstract: This article reports for the first time the anodic stripping voltammetric (ASV) detection of Zn at a gold disk macroelectrode for the analysis of fuel bioethanol. The accurate determination of Zn at gold macroelectrodes was only possible with the aid of batch injection analysis (BIA) associated with ASV; this statement was proved by comparison with a conventional three-electrode system. The BIA system consisted of injections of bioethanol sample plugs (up to 1 mL) at 28.3 μL s"−"1 directly onto a working (gold disc) electrode immersed in 0.04 mol L"−"1 Britton-Robinson buffer (pH 7) solution through an electronic micropipette and the Zn deposition occurs simultaneously. The highest analytical response for Zn was obtained for a deposition time of 90 s, which indicated that Zn deposition also occurred from diffusion after the injection ended. The proposed method presented a low detection limit (5 μg L"−"1), a linear range between 25 and 250 μg L"−"1, and adequate recovery values (88–104%) for spiked samples, but no sample treatment was required. Such remarkable analytical features associated with the portability characteristics of BIA demonstrated the promising application of the proposed method for routine and on-site determination of metals in fuel bioethanol

[en] Highlights: • Electrochemical sensing of antibiotic (6 classes) residues in milk within 2016–2020. • Strategies focusing nanomaterials and composites for improved detectability. • Molecularly imprinted polymers (MIPs) and aptamers providedexcellent selectivity. • Sample preparation plays a key role according to detection potential and voltammetric profile. • Fabrication of low-cost sensors and rationalized synthesis of MIPs are new trends. Several antibiotics have been applied to veterinary medicine due to their broad-spectrum of antibacterial activity and prophylactic power. Residues of these antibiotics can be accumulated in dairy cattle, in addition to promoting contamination of the environment and, in more serious cases, in milk, causing a public health problem. Different regulatory agencies establish maximum residue limits for these antibiotics in milk, so it becomes important to develop sensitive analytical methods for monitoring these compounds. Electrochemical techniques are important analytical tools in analytical chemistry because they present low cost, simplicity, high sensitivity, and adequate analytical frequency (sample throughput) for routine analyses. In this sense, this review summarizes the state of the art of the main electrochemical sensors and biosensors, instrumental techniques, and sample preparation used for the development of analytical methods, published in the last five years, for the monitoring of different classes of antibiotics: aminoglycosides, amphenicols, beta-lactams, fluoroquinolones, sulfonamides, and tetracyclines, in milk samples. The different strategies to develop electrochemical sensors and biosensors are critically compared considering their analytical features. The mechanisms of electrochemical oxidation/reduction of the antibiotics are revised and discussed considering strategies to improve the selectivity of the method. In addition, current challenges and future prospects are discussed.

[en] Highlights: • Highly-sensitive detection of TNT on rGO/MWCNT nanocomposite sensor. • Thin film of rGO/MWCNT formed at the immiscible interface of a biphasic solution. • Film transferred to a boron-doped diamond (BDD) electrode for TNT detection. • Electrochemical impedance spectroscopy showed faster electron transfer on rGO/MWCNT. • Field submicromolar detection of TNT, promising for forensic police intelligence. - Abstract: This work presents the highly-sensitive detection of 2,4,6-trinitrotoluene (TNT) on reduced graphene oxide/multi-walled carbon nanotube (rGO/MWCNT) nanocomposite sensor. The formation of a thin film of this nanocomposite occurred at the cyclohexane/water immiscible interface of a mixture of MWCNT and rGO in the biphasic solution. The film was transferred to a boron-doped diamond (BDD) electrode for the square-wave voltammetric detection of TNT, which presented improved analytical characteristics in comparison with bare BDD and after modification with precursors. Electrochemical impedance spectroscopy also revealed the faster electron transfer for a redox probe on the nanocomposite modified surface. The synergistic properties of both carbon nanomaterials in the thin film modified surface resulted in a TNT sensor with a detection limit of 0.019 µmol L^-1 within a wide linear range (0.5–1100 µmol L^-1), with superior performance in comparison with other electrochemical sensors produced with carbon nanomaterials. This new material provides great promises for the highly-sensitive detection of other nitroaromatic explosives as well as other analytes. Moreover, the interfacial method enables the production of homogeneous and stable films on large coated areas as well as the large-scale production of electrochemical sensors.

[en] Highlights: • Electrochemistry of phenolic compounds on Double-walled carbon nanotubes (DWCNTs). • Functionalization inserted defects on structure but also decreased electroactive area. • Increased voltammetric signals seem to be effect of electroactive area. • Intense decrease in surface area (BET analysis) of shorter lengths DWCNTs. • Non-functionalized DWCNT provided higher amperometric sensitivity under flow system. -- Abstract: Double-walled carbon nanotubes (DWCNTs) of different length were submitted to acid functionalization and investigated as chemical modifiers on glassy-carbon electrode (GCE) for the sensing of dopamine and catechol. Acid functionalization introduced oxygenated groups and defects on the structure of DWCNTs, as detected by infrared, Raman and X-ray photoelectron spectroscopy. However, cyclic voltammetric experiments showed higher current responses on non-functionalized (NF) DWCNTs. The decrease in response was stronger for shorter length nanotubes (S-DWCNT) modified GCE, which was attributed to the reduction of electroactive area of functionalized nanotubes after acid treatment with HNO₃/H₂SO₄. Brunauer-Emmett-Teller (BET) analyses confirmed the decrease in surface area of functionalized (F) DWCNTs, especially on FS-DWCNT. Amperometric measurements also showed decrease in sensitivity and higher detection limit values on the FS-DWCNT, which is also due to the decrease in electroactive area. As conclusion, DWCNT is a potential carbon-based material to the development of highly sensitive amperometric sensors and acid functionalization is not likely required due to the higher surface area provided by modification with the untreated material.

[en] This work presents the potential application of organic-resistant screen-printed graphitic electrodes (SPGEs) for fuel analysis. The required analysis of the antioxidant 2,6-di-tert-butylphenol (2,6-DTBP) in biodiesel and jet fuel is demonstrated as a proof-of-concept. The screen-printing of graphite, Ag/AgCl and insulator inks on a polyester substrate (250 μm thickness) resulted in SPGEs highly compatible with liquid fuels. SPGEs were placed on a batch-injection analysis (BIA) cell, which was filled with a hydroethanolic solution containing 99% v/v ethanol and 0.1 mol L"−"1 HClO_4 (electrolyte). An electronic micropipette was connected to the cell to perform injections (100 μL) of sample or standard solutions. Over 200 injections can be injected continuously without replacing electrolyte and SPGE strip. Amperometric detection (+1.1 V vs. Ag/AgCl) of 2,6-DTBP provided fast (around 8 s) and precise (RSD = 0.7%, n = 12) determinations using an external calibration curve. The method was applied for the analysis of biodiesel and aviation jet fuel samples and comparable results with liquid and gas chromatographic analyses, typically required for biodiesel and jet fuel samples, were obtained. Hence, these SPGE strips are completely compatible with organic samples and their combination with the BIA cell shows great promise for routine and portable analysis of fuels and other organic liquid samples without requiring sophisticated sample treatments. - Highlights: • Organic-resistant screen-printed graphitic electrodes (SPGE) for (bio)fuels. • Screen-printing of conductive and insulator inks on thin polyester substrate. • Continuous detection of antioxidants in electrolyte with 99% v/v ethanol. • SPGE coupled with batch-injection analysis allows over 200 injections (100 μL). • Similar results to GC and HPLC analyses of biodiesel and aviation jet fuels.

[en] We report for the first time a rapid preparation of Zn_1_−_2_xCo_xNi_xO nanoparticles via a versatile and environmentally friendly route, microwave-assisted hydrothermal (MAH) method. The Co, Ni co-doped ZnO nanoparticles present an effect on photoluminescence and electrochemical properties, exhibiting excellent electrocatalytic performance compared to undoped ZnO sample. Photoluminescence spectroscopy measurements indicated the reduction of the green–orange–red visible emission region after adding Co and Ni ions, revealing the formation of alternative pathways for the generated recombination. The presence of these metallic ions into ZnO creates different defects, contributing to a local structural disorder, as revealed by Raman spectra. Electrochemical experiments revealed that the electrocatalytic oxidation of dopamine on ZnO attached to multi-walled carbon nanotubes improved significantly in the Co, Ni co-doped ZnO samples when compared to pure ZnO. - Graphical abstract: Rapid synthesis of Co, Ni co-doped ZnO nanoparticles: optical and electrochemical properties. Co, Ni co-doped ZnO hexagonal nanoparticles with optical and electrocatalytic properties were successfully prepared for the first time using a microwave hydrothermal method at mild conditions. - Highlights: • Co"2"+ and Ni"2"+ into ZnO lattice obtained a mild and environmentally friendly process. • The heating method strongly influences in the growth and shape of the particles. • Short-range defects generated by the ions insertion affects the photoluminescence. • Doped ZnO nanoparticles improve the electrocatalytic properties of pure oxide

[en] This work describes an efficient, fast, and reliable analytical methodology for mercury determination in urine samples using stripping chronopotentiometry at gold film electrodes. The samples were sonicated in the presence of concentrated HC1 and H₂O₂ for 15 min in order to disrupt the organic ligands and release the mercury. Thirty samples can be treated over the optimized region of the ultrasonic bath. This sample preparation was enough to allow the accurate stripping chronopotentiometric determination of mercury in the treated samples. No background currents and no passivation of the gold film electrode due to the sample matrix were verified. The samples were also analyzed by cold vapour atomic absorption spectrometry (CV-AAS) and good agreement between the results was verified. The analysis of NIST SRM 2670 (Toxic Metals in Freeze-Dried Urine) also validated the proposed electroanalytical method. Finally, this method was applied for mercury evaluation in urine of workers exposed to hospital waste incinerators

[en] This work presents a novel electrochemical method for the determination of oxcarbazepine (OXC) in urine and pharmaceutical samples using a flow injection analysis (FIA) system coupled to multiple-pulse amperometric (MPA) detection on a boron-doped diamond electrode (BDDE). The unique voltammetric profile of OXC on the BDDE, consisting of two electrochemical oxidation processes between +1.6 and +1.8 V versus Ag/AgCl/3.0 mol L⁻¹ KCl generating cationic radical species that undergo two electrochemical reduction processes at −0.2 and −1.0 V, was used for the application of MPA detection for the selective detection of OXC in biological samples. Briefly, OXC determination consisted in the application of a three-potential waveform: (1) at +1.7 V/200 ms, generator potential pulse for oxidation of OXC; (2) at −1.1 V/30 ms, collector potential pulse for reduction of the generated product and OXC quantification; (3) at −1.3 V/300 ms, potential pulse for cleaning the BDDE. This strategy enabled OXC determination in urine free from the interference of ascorbic and uric acids. The method showed high repeatability (RSD −1 OXC), high analytical frequency (65 determinations per hour), wide working linear range (from 2.0 to 80.0 μmol L⁻¹) with a limit of detection of 0.42 μmol L⁻¹ under optimized FIA conditions (sample loop: 200 μL and flow rate: 3.5 mL min⁻¹), and recovery values close to 100% in all analyses.