Voltammetric detection of vitamin B1 (thiamine) in neutral solution at a glassy carbon electrode:Via in situ pH modulation

Voltammetric analysis is often dependent on pH and on the addition of buffer reagents to optimise the analytical procedure. This approach is not always possible for in situ analytical measurements, for example when studying biological fluids or ingredients in food. Therefore, a method is proposed herein, which employs a working electrode to do both, that is, to locally modulate the pH value and to measure the analytical response. As a model system, thiamine (vitamin B1) is detected in aqueous KCl with a pH modulation brought about with negative potentials applied to the working electrode. Interferences from ascorbic acid and uric acid are considered. Exploratory data are presented and methods for improving the detection limit are suggested. Their potential for applications in electroanalysis (and in a broader range of processes) is discussed and the detection of thiamine in rice is demonstrated.</p

Surface modified carbon nanomats provide cationic and anionic rectifier membranes in aqueous electrolyte media

Carbon nanofibers (CNFs) are converted into anionic current rectifiers by surface modification with amine functional groups using hydrothermal means (forming modified CNFs, with generation-3 poly (propylene imine) dendrimer, urea and boric acid). To confirm surface charge, morphological changes and carbon nanomat thickness, zeta potential analysis, transmission electron microscopy (TEM) and scanning electron microscopy (SEM), were used. When a dispersion of surface modified carbon nanofibers in DMF is drop-cast asymmetrically to form nanomats onto laser drilled microholes (5, 10, or 20 µm diameter) of poly (ethylene terephthalate) substrates and immersed into aqueous electrolyte solutions, anionic diode behaviour is observed (in contrast to pristine carbon nanofibers, which exhibit cationic diode behaviour). The effects of electrolyte type, ionic strength, and microhole diameter on ionic diode performance were investigated using cyclic voltammetry, chronoamperometry, and impedance spectroscopy. Future applications in desalination are proposed

Cationic Rectifier Based on a Graphene Oxide-Covered Microhole:Theory and Experiment

Cation transport through nanochannels in graphene oxide can be rectified to give ionic diode devices for future applications, for example, in desalination. A film of graphene oxide is applied to a 6 μm thick poly(ethylene terephthalate) substrate with a 20 μm diameter microhole and immersed in aqueous HCl solution. Strong diode effects are observed even at high ionic strength (0.5 M). Switching between open and closed states, microhole size effects, and time-dependent phenomena are explained on the basis of a simplified theoretical model focusing on the field-driven transport within the microhole region. In aqueous NaCl, competition between Na + transport and field-driven heterolytic water splitting is observed but shown to be significant only at low ionic strength. Therefore, nanostructured graphene oxide is demonstrated to exhibit close to ideal behavior for future application in ionic diode desalination of seawater. </p

Cationic Rectifier Based on a Graphene Oxide-Covered Microhole:Theory and Experiment

Cation transport through nanochannels in graphene oxide can be rectified to give ionic diode devices for future applications, for example, in desalination. A film of graphene oxide is applied to a 6 μm thick poly(ethylene terephthalate) substrate with a 20 μm diameter microhole and immersed in aqueous HCl solution. Strong diode effects are observed even at high ionic strength (0.5 M). Switching between open and closed states, microhole size effects, and time-dependent phenomena are explained on the basis of a simplified theoretical model focusing on the field-driven transport within the microhole region. In aqueous NaCl, competition between Na + transport and field-driven heterolytic water splitting is observed but shown to be significant only at low ionic strength. Therefore, nanostructured graphene oxide is demonstrated to exhibit close to ideal behavior for future application in ionic diode desalination of seawater. </p

Development of Differential Pulse Anodic Stripping Voltammetry Technique for Cadmium(II) Detection and Its Application in Water Spinach

Cadmium is a toxic pollutant that is harmful to the environment and humans. The purpose of this research was to develop a method for cadmium(II) detection using differential pulse anodic stripping voltammetry (DPASV) using a glassy carbon electrode. The developed method was then applied for cadmium detection in the vegetable samples which is water spinach. The developed method was optimized in several parameters such as potential window, deposition potential, deposition time, and scan rate. The developed method for cadmium(II) detection was also investigated in its analytical performance includes linearity, precision, detection limit, and quantitation limit. The optimum conditions for cadmium(II) detection in 0.1 M KCl using DPASV technique obtained such as potential window from -1200 to -100 mV, deposition potential of -1100 mV (vs Ag/AgCl), and deposition time of 360 s. It was obtained good linearity for cadmium(II) detection using the DPASV technique with an&nbsp;R2 of 0.996. The precision was expressed as %SBR with 0.66%. The detection and quantitation limits for cadmium(II) detection were 0.4206 µM~0.0771 ppm and 0.5525 µM~0.1013 ppm, respectively. The developed method was then applied for cadmium(II) measurement in the water spinach sample and the obtained cadmium(II) concentration in water spinach was 0.2399 mg/Kg

CARBON PASTE ELECTRODE HEXADECYLTRIMETHYLAMMONIUM BROMIDE MODIFIED NATURAL ZEOLITE FOR CHROMIUM(VI) DETECTION

A simple voltammetric technique for quantification of chromium(VI) is presented in this work. The technique is based on linear sweep voltammetric reduction Cr(VI) on hexadecyltrimethylammonium bromide (HDTMABr) modified Lampung zeolite carbon paste electrode. Selected HDTMABr concentration for natural zeolite modification is obtained 200 mM. Working electrode for chromium(VI) detection is made by graphite, paraffin oil and HDTMABr modified Lampung zeolite. The effect of supporting electrolyte matrix, pH and also scan rate is also investigated. The calibration curve for chromium(VI) detection using the proposed method shows linearity from 0.2 to 1.0 mM with sensitivity, detection and quantification limit, and precision was 0.4294 mM, 3.63 x 10-4 mM, 1.197 x 10-3 mM, 4.49%, respectively

A Brief Review on Fabrication of Screen-Printed Carbon Electrode: Materials and Techniques

Screen-printed carbon electrode (SPCE) is one of the most interesting designs to combine a working (from carbon based material), reference, and counter electrode in a single-printed substrate. SPCE has been used in many electrochemical measurements due to its advantages for analysis in microscale. This paper summarises the main information about SPCE fabrication from the material and fabrication technique aspect on the flat substrate based on the work that has been published in the last 30 years. The success of SPCE fabrication is highly dependent on the composition of conductive ink which consists of conductive materials, binder, and solvents; substrate; and fabrication techniques. Among the carbon-based materials, the most widely used for SPCE fabrications are graphite, graphene, and carbon nanotubes. The frequent binder used are polymer-based materials such as polystyrene, polyaniline, poly 3,4-ethylenedioxythiophene:polystyrene sulfonate (PEDOT:PSS), and polyvinyl chloride. The solvents used for SPCE fabrication are varied including water and various organic solvents. The main characteristics of the SPCE substrate should be inert in order to avoid any interferences during electrochemical measurements. The screen printing and inkjet printing technique are preferred for SPCE fabrication due to easy fabrication and the possibility for mass production of SPCE

Extraction of Hydrophobic Analytes from Organic Solution into a Titanate 2D-Nanosheet Host: Electroanalytical Perspectives

Titanate nanosheets (single layer, typically 200 nm lateral size) deposited from aqueous colloidal solution onto electrode surfaces form lamellar hosts that bind redox active molecular redox probes. Here, hydrophobic redox systems such as anthraquinone, 1-amino-anthraquinone, deca-methylferrocene, 5,10,15,20-tetraphenyl-21H,23H-porphine manganese (III) chloride (TPPMnCl), and α-tocopherol are shown to bind directly from cyclopentanone solution (and from other types of organic solvents) into the titanate nanosheet film. For anthraquinone derivatives, stable voltammetric responses are observed in aqueous media consistent with 2-electron 2-proton reduction, however, independent of the pH of the outside solution phase environments. For decamethylferrocene a gradual decay of the voltammetric response is observed, but for TPPMnCl a more stable voltammetric signal is seen when immersed in chloride containing (NaCl) electrolyte. α-Tocopherol exhibits chemically irreversible oxidation and is detected with 1 mM–20 mM linear range and approximately 10 −3 M concentration limit of detection. All redox processes exhibit an increase in current with increasing titanate film thickness and with increasing external electrolyte concentration. This and other observations suggest that important factors are analyte concentration and mobility within the titanate host, as well as ion exchange between titanate nanosheets and the outside electrolyte phase to maintain electroneutrality during voltammetric experiments. The lamellar titanate (with embedded tetrabutyl-ammonium cations) behaves like a hydrophobic host (for hydrophobic redox systems) similar to hydrophobic organic microphase systems. Potential for analytical applications is discussed. </p

Cationic diodes by hot-pressing of Fumasep FKS-30 ionomer film onto a microhole in polyethylene terephthalate (PET)

A cationic diode is fabricated by hot-pressing a commercial cation-conducting ionomer membrane (Fumasep FKS-30) onto a polyethylene terephthalate (PET) substrate with microhole of 5, 10, 20, or 40 mu m diameter. Both, symmetric (ionomer on both sides) and asymmetric (ionomer only on the working electrode side) cases are investigated in a 4-electrode measurement cell. A 5-electrode measurement cell in generator-collector mode is employed to directly detect competing proton transport through the ionomer. Only the asymmetric device allows ion current rectification to be observed. With decreasing microhole diameter the rectification effect increases. With increasing electrolyte concentration (for aqueous HCl, NaCl, LiCl, NH4Cl, MgCl2, CaCl2) the rectification effect diminishes. Competition between cation transport and proton transport is observed in all cases. A qualitative impedance model is developed to diagnose the quality and performance of these cationic diodes.</p