Simultaneous determination of direct yellow 50, tryptophan, carbendazim, and caffeine in environmental and biological fluid samples using graphite pencil electrode modified with palladium nanoparticles.

The present study reports the development of graphite pencil electrode modified with palladium nanoparticles (PdNPs) and its application as an electrochemical sensor for the simultaneous detection of direct yellow 50, tryptophan, carbendazim and caffeine in river water and synthetic urine samples. The combination involving the conductive surface of the graphite pencil electrode (GPE) and the enlargement of the surface area caused by the use of palladium nanoparticles (PdNPs) led to the improvement of the analytical performance of the proposed device. The surface of the GPE-PdNPs was characterized by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The charge transfer kinetics of the electrode was evaluated based on the electrochemical analysis of the potassium ferricyanide redox probe. Using square wave voltammetry (SWV), well-defined and fully resolved anodic peaks were detected for the analytes, with peak-to-peak potential separation not less than 200 mV. Under optimised conditions, the following linear range concentrations were obtained: 0.99-9.9 µmol L-1 for direct yellow 50; 1.2-12 µmol L-1 for tryptophan; 0.20-1.6 µmol L-1 for carbendazim; and 25-190 µmol L-1 for caffeine. The sensor showed good sensitivity, repeatability, and stability. The device was successfully applied for the determination of analytes in urine and river water samples, where recovery rates close to 100% were obtained. Due to its low cost and reusability by simple polishing, the sensor has strong potential to be used as an electrochemical sensor for the determination of different analytes.

Simultaneous determination of environmental contaminants using a graphite oxide - Polyurethane composite electrode modified with cyclodextrin.

A composite electrode based on graphite oxide (GrO)-polyurethane (PU) modified with ß-cyclodextrin (CD) was proposed for the simultaneous determination of three drugs: terbutaline (TER), nimesulide (NIM), and methocarbamol (MET), as possible contaminants in river water samples. To evaluate the performance of the proposed CD-GrOPUE, voltammetric techniques were used and two other electrodes were fabricated (GrOPUE and GrPUE) for comparison. The functionalization of the GrO was confirmed by scanning electron microscopy images, energy-dispersive X-ray spectroscopy analysis, and thermogravimetry. Cyclic voltammograms obtained for TER, NIM, and MET indicated an irreversible behaviour at 0.6 V, 0.9 V and 1.2 V (vs. Ag/AgCl (3 mol L-1 KCl)), respectively, on each working electrode, with the highest peak current values been obtained using the CD-GrOPUE. Under optimal conditions, using square-wave voltammetry, the linear ranges obtained (and limit of detection) for TER, NIM, and MET were 2.5-30 (0.55), 0.62-7.3 (0.083), and 0.62-7.3 (0.077) µmol L-1, respectively. The analytical method developed were applied in the simultaneous determination of TER, NIM, and MET in river water samples, with results like those obtained using a reference spectrophotometric method (at a confidence level of 95%). One can conclude, that the modification of GrO with CD arrays made possible the development of a robust and simple sensor platform for environmental analyses.

Simultaneous voltammetric sensing of levodopa, piroxicam, ofloxacin and methocarbamol using a carbon paste electrode modified with graphite oxide and ß-cyclodextrin.

A carbon paste electrode (CPE) was modified with graphite oxide (GrO) and ß-cyclodextrin (CD) to obtain a sensor for simultaneous voltammetric determination of levodopa (LD), piroxicam (PRX), ofloxacin (OFX) and methocarbamol (MCB). The morphology, structure and electrochemical properties of the functionalized GrO were characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy, contact angle measurements and cyclic voltammetry. Under the optimal experimental conditions, the sensor is capable of detecting LD, PRX, OFX and MCB by square wave voltammetry (SWV) at working potentials of +0.40, +0.60, +1.03 and + 1.27 V (versus Ag/AgCl), respectively. Response is linear from 1.0 to 20 µM for LD, from 1.0 to 15 µM for PRX, from 1.0 to 20 µM for OFX, and from 1.0 to 50 µM for MCB. The respective limits of detection are 65, 105, 89 and 400 nM. The method was successfully applied to the simultaneous determination of LD, PRX, OFX and MCB in (spiked) real river water and synthetic urine samples, and the results were in agreement with those obtained using a spectrophotometric method, with recoveries close to 100%. Graphical abstract Schematic presentation of a novel electroanalytical method employing a carbon paste electrode modified with graphite oxide and ß-cyclodextrin for the simultaneous determination of levodopa, piroxicam, ofloxacin and methocarbamol in urine and river water samples by square wave voltammetry.

Square-wave adsorptive anodic stripping voltammetric determination of norfloxacin using a glassy carbon electrode modified with carbon black and CdTe quantum dots in a chitosan film.

A glassy carbon electrode was modified with carbon black and CdTe quantum dots in a chitosan film to obtained a sensor for norfloxacin (NOR) in the presence of dopamine, caffeine, and uric acid. The morphological, structural and electrochemical characteristics of the nanostructured material were evaluated using spectrophotometry, X-ray diffraction, transmission electronic microscopy and voltammetry. The high electrochemical activity, fast electron transfer rate and high surface area enhanced the oxidation peak currents and shifted the peak potentials of NOR for more negative values (typically at 0.95 V vs. Ag/AgCl). Electrochemical determination of NOR was carried out using square-wave adsorptive anodic stripping voltammetry (SWAdASV). Response is linear in the 0.2 to 7.4 µmol L-1 NOR concentration range, and the detection limit is as low as 6.6 nmol L-1. The method was successfully applied to the determination of norfloxacin in pharmaceutical formulation, synthetic urine and spiked serum. Graphical abstract Schematic presentation of a voltammetric method using a glassy carbon electrode modified with carbon black and CdTe quantum dots in a chitosan film for the determination of norfloxacin in serum and urine samples.

Simultaneous determination of isoproterenol, acetaminophen, folic acid, propranolol and caffeine using a sensor platform based on carbon black, graphene oxide, copper nanoparticles and PEDOT:PSS.

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%.